Kitten introductions - what to do next?

Hello! I'm a new kitten mama. I've always wanted a cat but hadn't been able to because of allergies. But a few months ago, I found a tiny stray kitten all by itself outdoors, and decided to take her in. I had no idea about kittens or cats at the time. My allergies acted up a little bit, but I'm not affected by my kitty at all now, for which I'm grateful It turned out that TT was around 5 weeks old when I found her, and she's 13 weeks old now. I took her to the vet right away and she seemed in good health; treated for worms, fleas. It turned out she had an intestinal parasite, and then a URI, so it had been a couple of weeks of meds for these different conditions. She hasn't been spayed yet because she has been on meds, and she's scheduled for one in 2 weeks.

TT has a lot of play-aggression; gnawing on my hands and feet when she's in the mood for play. And while I'm at home for frequently now, I won't be in the coming months. So, I decided to adopted another kitten similar in age, in hopes that TT will have a kitty companion and correct her play-aggression issue a bit. I adopted CC around 4 days ago. I thought of adopting a male kitten because I've read that male/female pairings go over well better, but at the adoption center, I felt that CC's personality, female kitten at 9 weeks old, would be better for TT's temperament. (Well, I had found a male kitten that I thought would match TT's mellow yet somewhat skittish temperament, but I was advised that he's still a bit feral and needs more socializing.)

TT was separated from her littermates while very young, and she hasn't interacted with another cat since I've had her. She's very sweet and careful, she takes her time getting used to situations. She loves shaded hidden areas and has various hiding places that she likes to lounge on. She doesn't actively meow except for food in the mornings, or whenever I'm in the kitchen and she's hungry. She doesn't hiss or bite when she's agitated but she will grumble/growl. I can't pick her up for more than a minute or two before she wants to be let down, but I'm allowed to pet her for a good amount of time while she sleeps with her body against mine when I'm sitting the couch. She loves playing with interactive fishing pole toys and isn't too engaged with playing by herself. When she's in play mode and I want to pet her, she immediately starts to try to gnaw on my hands, or I could be petting her and she turns over on her back so that she can try to gnaw on my fingers while kicking it with her back legs; she's sooo sweet when she's sleeping, but TT in play mode is me trying to distance my hands from her with a toy, and her reaching for my hands anyway. She runs up to me at the door whenever I come home and call her name.

CC was living in the same large cage with her two other litter mates; they'd sleep squished together in a hammock. She has already been spayed, she was spay three days before I adopted her. She's very well socialized, fearless, hammy, and loves being petted and cuddled with, and twists and turns over onto her back because she loves getting her belly rubbed. She plays very well by herself with mice toys and balls. I've isolated her in the bathroom for now so I'm still getting to know her.

TT and CC have already seen each other; it was a mistake on my part. I had intended to do scent introductions first and then eventually have them take a look at each other, but on that first night, when I was taking CC into the bathroom and moving things around, TT and CC caught sight of each other. TT reacted with startled wide eyes but didn't hiss and growl until CC started approaching her to play (her tail straight up in the air). CC, because she's such a ham, just wants to play with TT; I think she misses having companions around her as she had with her littermates. CC ran around the place like it was no big deal, whereas, when TT was initially getting acclimated, she was so careful and tentative about exploring her new digs. TT wasn't having it, and she followed/chased(?) CC around before I could separate them. Since then, I've swapped their scents, and also, have site-swapped a few times by placing TT in CC's safe zone/bathroom and CC in the living room (I'm with CC for 15 min, TT for 15, for a total of 30 min of site swapping a day).

Both TT and CC eat right by the door. TT has been reluctant, and while she does eat right by the door, she only eats half of her food; she'll eat from my hand literally an inch away from her food bowl, but she won't eat from her food bowl after a couple of bites. CC doesn't care, she eats wherever and whenever she's hungry; she sometimes purrs and rubs her body against the door because she can't wait to play with TT. TT is almost entirely on wet food, and likes dry food as a treat (I tried free-feeding dry food, but TT liked it too much and would eat the dry food over her wet food, so I took it away). It looks like CC has been on free-fed dry food, with a small amount of wet food twice a day, and I've been trying to get her on a mostly wet food diet, which I think she's also a little reluctant of but she's eating well. So, I have been enticing them by placing dry food right near the crack of the bathroom door, and TT will reach for and eat the dry food that's under the crack of the door with CC right in front of her on the other side, but TT's reluctant about her wet food for some reason.

They can reach their paws in under the crack of the bathroom door, and do so without hissing. I've opened the door a little bit so that they reach in with their paws through the opening. TT hisses and growls once or twice, but that's it. TT also sometimes sits right by the door and watches it as if to guard it from CC coming out. If I'm in the bathroom playing with CC, TT will be sitting right outside the door half the time, sticking her paws under the door sometimes. TT is curious by CC and sniffs her when she can, but is easily startled when CC reaches for her, either to play or in being defensive. TT approaches CC very cautiously, but CC is fairly unfazed but I think she's feeling a bit more wary now. This is where I'm starting to get more unsure. Because, they're eating by the door, they're reaching their paws for each other by the door opening in more of a curious way, though it can escalate to be more fight-y way, which I try to stop. I tried to have some supervised play time with the both of them today. CC was easily distracted by the fishing pole toy, but TT had her eyes trained on CC, which wasn't that bad, because CC was distracted from being her hammy self to TT, and thus, aggravating/startling TT.

But are supervised play times too soon? Should I wait until TT is fully comfortable to eat her food? Or until they stop pawing at each other at the door? When would be the right time to move on to a screen door so that they can fully see each other as they eat next to each other? I feel mostly focused on helping TT feel acclimated, because CC seems like she's ready to play and interact, but are there other things I should be doing for CC (of course, other than giving her general care, attention, and food)? I'm not really sure how long to keep up with this separation until it feels right for TT; how will I know when she's ready? I bought Feliway spray and have been spraying it on the door once a day, but I don't really know if it's helping. I also feel guilty that CC is being isolated in the bathroom, she must feel so lonely! Especially because I'm not in there with her as much as I am by my desk, while TT has free rein of the place to sit next to me or sit by the window or whatnot. I feel like CC has so much play and cheer in her and she's not getting as much of it from me or TT that she can. Thanks to folks who've taken the time to read this. I'm pretty puzzled as to my next steps.

TT also meows at the door when she knows I'm there with CC, and they both try to climb the door opening trying to get to each other... but I don't know what this means, if it's tentatively aggressive or playful.

If I have read correctly, TT eats her wet food (without growling/hissing?) ok, she just doesn't finish her portion?

I think that is ok. By your description, TT likely didn't have much socialization prior to you taking her home, and is, by nature, a more timid kitten. All things considered, I think progress is good.

You've only had CC for 4 days, which is not a very long time at all, especially in cat time. I would wait a bit to move forward until TT is more comfortable eating her food.

What you can do is more site swapping if possible. Maybe increase this to 2-3 days a day and/or longer sessions. Maybe even do feedings in opposite positions (TT in bathroom, CC outside the door).

I highly suspect these two will be integrated fully within the next week or two. Younger kittens typically adapt quicker to new cats. Your only negative is that TT really doesn't have much cat experience to pull from and her cat language likely isn't there. BUT, this will change over the next few months as the girls interact.

One suggestion...
Investing in some Feliway diffusers may very well be beneficial for TT. The spray is good for use in carriers for trips to the vet and other short term things; but, you would need to spray the area several times a day to get the full benefit.

I would get a diffuser for the bathroom, 1 for the hallway and maybe 1 for the main area of the house that TT spends her time. I think either the original Feliway or the MultiCat would be fine to use. (I know Petco was having a buy 1 get 1 50% off. I'd check there first if you have one around.)

Yes! TT has hesitancies about the general vicinity of the door (like when she's running around to play, she slows downs while in this area, and stuff like that). But she doesn't hiss when she eats her wet food, or her dry food treats, by the door. She just hasn't been finishing her portions ...and then she follows me to the kitchen meowing that she's hungry.

Okay, I will definitely do more site swapping and the swapped feeding positions. I have thought about the diffuser, the price was deterring me, but maybe I will buy a month-supply to help TT get more acclimated. Thank you so much!!

A positive update (I think)!

I bought some feliway diffusers yesterday afternoon and hoped for a good day today.

TT hadn't gotten back into the habit of finishing her wet food portions yet, but it seems like there may have been some different stressors for TT that could have dissuaded her from eating, than just a new kitten companion. Yesterday morning, I noticed some mangled multi-color fabric on the floor, it smelled a bit like cat food; I later realized that they were the tails for two identical mouse toys. TT must have chewed them off and swallowed them, and then threw it back up all without me realizing until the deed was done. I threw away the toys, and all the mice toy tails are accounted for, so I'm not worried about any bowel obstructions for TT, but I feel that she was definitely nervous about her throwing up this furry fabric. Also, today, she continued to resist eating the wet food (natural balance wild pursuit, that I had more recently included in her diet), but strangely enough so was CC, who eats everything. So, I changed both of their wet foods to a different brand in a duck recipe. CC gobbled up the duck wet food, and TT started to eat, but threw it up right away and refused to eat more. But she was interested to eat some dry food, and was drinking water throughout the day. So, I now have a sneaking suspicion that TT may have a food intolerance to duck (?) (she had previously thrown up this duck wet food once before, but ate it well at all the other times).  As a last ditch effort, I changed out TT's bowl again to fish wet food. She was interested to that right away and ate it up! I'm thinking that her lack of appetite was partly caused by her digestive troubles, coupled with her confusion of CC. I'll continue monitoring her feedings in the coming days, but I'm hoping that she's starting to feel better from today onward.

This morning, TT and CC were pawing at the door again. TT was meowing through the door, and neither of them were eating because they were both distracted by each other. I had this instinct that it may be okay for them to meet... so I opened the door. Once CC came out of the bathroom, TT immediately pounced and they were sprinting across the place from room to room chasing each other. I was so taken aback by their sudden burst of energy, what they were doing looked kind of scary (like they were fighting, biting) but I wondered if they were being aggressive because it didn't feel like it. I immediately reached for my water squeeze bottle to try to break it up, but I didn't know if I should. So, puzzled, while these two kitties were sprinting across everywhere, tumbling around, kicking each other's faces, and biting each other's necks, I was Googling "kittens playing or fighting?" on my phone. And it seemed like they were playing; they were completely silent apart from the occasional growling, they were switching off on chasing each other, I separated them once (held one and then the other) but they just wanted to be let down from my arms to continue interacting with each other. TT is physically bigger, around 3.8 lbs to CC's 2lbs, so I'm a little worried about TT being able to hold back but it doesn't seem like an issue at the moment. They did this for hours, literally. They'd take resting and water breaks now and again, but they were sprinting full speed and tumbling around for ages.

I think TT eventually established dominance because I later found them on the cat tree with TT at the top platform and CC at the bottom platform. They're friends, I think! They certainly seem comfortable with each other. TT doesn't get startled by CC's movements anymore. I think TT is kind of obsessed with playing with CC at the moment. I tried to engage both of them in a fishing pole toy, TT's favorite, and TT just sat squarely looking at CC while CC was immersed in happily chasing the toy. I've seen TT sit from a distance just watching CC, and then, trying to engage in play with her. It seems like CC hisses when she's not in the mood and TT respects her wishes, but could this turn into bullying of CC by TT? Are there any signs I should be looking for, behavior-wise?

I am wondering if I should keep CC in the bathroom, with the door closed, during the night for the next couple of days. I feel like CC isn't quite acclimated to a routine; she doesn't always eat her wet food meals right away (I think this is because she was free-feeding dry food where she was previously at), I don't think she's drinking as much water as she could, I can't be sure that she's always using her litter box (though I think she is) or that she'll head over to her box whenever she has to do her business. Should I keep CC's door open or closed? If I keep the door open, should I keep their food bowls in separate rooms/areas now (instead of right next to each other)? And their litter boxes in more separated areas as well? I don't want to enable either one of them getting ambushed while they're eating or using their box. And CC seems to be interested in TT's bowl over her own, so I want to make sure that they're each eating their own portions.

Thank you for reading, folks! I'm so glad I have some good news to share.

So, new update, I guess the roles have switched a little bit?

TT is now completely comfortable with CC. She's so interested in wanting to spend any time she can near CC, and tries to climb on top of her to play with her and play-gnaw on her. CC is kind of exhausted with TT's hovering and when she has had enough, she hisses and growls at her. TT respects her hissing and stops, and then, 20 seconds to a couple of minutes later, resumes her play attempts. CC engages in play initiated by TT most of the time, but other times, she just wants to sleep and hang out, but TT's being a bit of a bother. So, I've separated them again for now.

CC is perfectly content in not being around TT, but TT clearly misses CC when she's separated from her and sometimes meows by her door (though, she will sit on her cat tree or by the window after waiting a while). TT is a pound or so bigger than CC, so I'm also worried that CC is getting play-gnawed a bit too much, as she's not the one who is initiating play the majority of the time. When I try to distract them with supervised play toys, CC gets interested in the toys but TT doesn't. Whereas, before, TT got startled whenever CC approached her, and it was more comfortable for TT to be around CC when CC was distracted with a toy. Now, when CC is distracted with a toy, it leaves CC vulnerable/distracted to getting play-pounced on by TT who continues to have her eyes trained on CC. I don't think this is bullying; just an over-eager TT, who used to be a stray and hasn't been around cats, wanting to hang around CC, a shelter kitty who has been around other cats all of her life and isn't as fazed/interested by other cats. Should I leave the place open to them to "work it out," or try to keep them separated until TT gets less obsessed with CC? I'm just concerned that unwanted attention from TT will stress CC out.