New declawed cat to clawed cat family?

Hey all! So I'm new here and because this covers SO much, I'm not totally sure where it fits in.

So here's the deal. I have a 1 and a half neutered male, Whiskey, and Badger, a 6 month kitten that will be getting fixed soon, both with their claws. Long story short, a neighbour moved out and kicked their older (then my pair) declawed and neutered cat outside. I call him Russia. The current crazy cat lady has been feeding him along with her pack of 12, but she intends to move out and take her 12 with her. (This is a side-by-side apartment by the way)
He's very skinny when he let me pet him and like I said, he's declawed and it gets freaking cold around here. Being the totat wuss that I am, I'm playing with the idea of adopting him into my house. Problem is, the only experience I've had with declawed cats is that all three of them were utterly vicious moody cranky hair balls.

The other thing is that when Russia fills out, he'll easily be twice the size of Whiskey. So I'm not worried about them beating on him. Problem is, Whiskey is completely laid back and Badger thinks everyone is his friend. Russia on the other hand, seems very bossy/dominant when I let him in for a bit just so they could smell each other ect.

What I've been doing so far is feed Russia outside to get him used to me. Now every day at 4 he's at my door waiting for food. I've opened the door a little so that he and my cats can smell each other and that gone well, he growls at them but that's about it. The other day I got my sister over to distract my cats while I let him inside to look around, smell everything, that kind of thing.
The next time I had my cats out and they got to kinda sniff each other but he got a little moody when Badger came up. He got smacked of course and turned tail while Badger sat off to the side not quite sure what to make of the stranger that was twice his size. The thing is, I've been bribing him with food to come inside.

This morning, I fed all three inside at the same time (my cats in one bowl, Russia off to the side) and was acting protective over his pile of food when my two wanted to smell him. He kinda scared Badger off to eat out of his bowl.

So, to sum it up all my questions.
Declared cats? Do they calm down eventually or will he always be a little moody? I have zero experience with them.
How do I get him to gain weight?
How do I make sure he doesn't bully my cats around because even though he's declawed, he way bigger then them.
Is he acting dominant because he's hungry or is that a declawed cat thing?
Should I be introducing them one at a time so he doesn't feel outnumbered and if so, who first?

Another problem that has me twitching is that I saw him marking outside. So how likely is he to mark inside to try and claim territory or is the fact my place smells of my cats good enough that he won't.

Thanks some much.

Marking cannot be predicted.  It totally depends on how the cats adjust.  Once the totem pole is arranged, who is top, middle and bottom, marking is less likely unless one is trying to move up in status. 

I have had a super sweet declawed cat who was a rescue from outside and did just fine with the clawed ones.  I clip all their claws weekly anyhow so it's not like they have daggers, and this poor guy was skinny and starving.  It sounds like yours is too, which is why he is protective of his food.  That will change once he always has enough food.  If the cat lady is just going to leave him behind, I would be like you and would adopt him and try to work things out between the cats.  If he doesn't fit in, you can probably find another adoptive home for him. 

Declawed cats are "special needs" cats often because they are often in pain.  However, there are many things to do to prevent pain and help with any problems, just work with your vet.  Not all declawed cats have pain, but many do.  They are not all grumpy but anyone in constant pain will be grumpy. 

Here is a good article to read.

http://www.allfelinehospital.com/declaws.pml

Also, introducing cats to cats -- you are doing it right, which is slowly.  Your instincts are good.  This may help.

http://www.thecatsite.com/a/how-to-successfully-introduce-cats-the-ultimate-guide

Red Top Rescue- thanks so much. I'm not a stranger to having cats around so I've gone through the whole introducing cats thing but they've all been young (year or less) and not such a size difference. As for declawed, yeah no experience. We had outside cats and never declawed any of our cats indoor or out door. Im glad to hear his attitude problem might just be because he's hungry and sick of dealing with 5 little siblings. (Crazy cat lady didn't have the money to spay her female and she got out of the house...) anyways, it's not so much of her leaving him behind so much as she owns her 12 and this big boy was kicked out of another place. She just leaves her door and a window open all summer/ fall so everyone comes and goes wether or not she actually owns them. ironic part is, we have the same name and I am WELL on my way to becoming the next crazy cat lady if and or when she moves out.

Anyways, back on topic. How would I tell if he was in pain? The only kind of 'pain' I've ever dealt with in a cat is the obviously visible ones outdoor cats will get. I haven't really noticed him favouring his feet and he still jumps up into the fence railing. He can see into my apartment that way, it's hilarious.

Heh, and the big stinker has figured out that it's warmer in my place then outside. Didn't have to bribe him to come inside today.
So would the best thing (if he's protective of his food) be to fatten him up a bit before seeing if he'll play nice? So far he just growls a lot unless my kitten gets to close. Little dweeb got clocked again. *sigh* kittens always think they are indistructable and that everyone is their best friend.

Just feed him in a private place, like a bathrrom or anywhere you can close the door.  Then remove the food and let him out.  Food is obviously something he has been short of and wants to protect.  What I see with the gang around here is that once everyone has their own place to eat, there is no fighting.

UPDATE

So everything's going good, he's filled out and isn't acting nearly as food protective, he's just grumpy. Might be because of the snow and it's obvious his feet are bothering him. He's limping. Now that they're all kinda used to each other, (read tolerate the other breathing the same air) he seems aloof. Want's nothing to do with the my two but it's Whiskey to my surprise that's the trouble maker. Mostly because he's such a mellow cat. Anyway, he managed to corner Russia under my headboard in my room and they had a little spat. They still glare at each other and Russia growls at everything but that seems pretty normal. He still hates being picked up, (to bad for him) and he does NOT play. I know with Badger and Whiskey i had them chasing the laser pointer till they were to tired to get mad at each other and it worked great, they're best friends now. Badger is convinced he and Russia are gonna be best friends and you can see him drooling over that big beautiful fluffy tail Russia has that is just BEGGING to be attacked. (he did that once and got smacked go figure) Russia and Whiskey are a different story. I've got them eating cat treats three inches away from each other and as long as i  keep the treats coming they're fine. But once the treats are gone Russia backs off to his personal bubble and just watched them. He won't let Whiskey smell him, they've both smelt stuff that the other has touched (Russia has a brush and Whiskey has the house). Guess I'm kinda asking how do i get them to interact with each other? Russia has no interest in playing, could that be his feet?

Have you had him checked over by a vet?  (I may have missed it if you said so.)  Cats all have different personalities.  Peaceful coexistence is sometimes all you can get between cats and thats ok.  One of my girls does not like the lazer pointer.  She would sit back and her sister go nuts over it.  She hid from catnip bubbles! But that also could have been because of her sister's crazy reaction!  She plays in different ways.  If you haven't already I would have his feet checked by a vet.  He may not b a playful kitty; but it would help you to know if he is in pain and then you could figure specific things to help ease his discomfort.  

moochnnoodles

No i haven't. "Technically" he isn't mine because the lady at the end of my apartment has "adopted" him into her pack. That being said, he's at my place WAY more often because then he only has to deal with two cats and ones scared of him. It's way more relaxed over here.

I would suggest having a friendly conversation with the lady who has "adopted" him into her pack.  I share a few outside cats with my neighbors and we converse about them.  I got one of them neutered, and he paid me to get the other one neutered (the third one we share was already neutered).  I do their flea medication and I wormed them all, and he took them for their booster shots.  You might offer to take him to your vet and get his feet checked because if he's limping, he's obviously in pain, and perhaps the vet could prescribe a safe long-term pain medication.  Also, the idea of her moving away and him being abandoned a second time is heartbreaking, and she may feel the same way.  You might agree that it is better for him to stay with you, and now that it's getting cold and her windows won't be open, it would be a good time to make him welcome in the warmth of your house.  If she has 12 cats, she loves cats, and the two of you could share this guy at least until she moves, and by then he will know he is YOUR cat and has not been abandoned again.

Apparently now she is not moving away which is great because then her cats can keep the mice out of my car The joke is, or not, is that if Russia's not locked inside her place, he's at mine. And i mean, all the time. He's either on the railing by the front door to watch me in the kitchen or on the railing by the back window so he can stare at me all evening. He knows i let him in and suckers me into it all the time. I think that's because he's just sick and tired of dealing with all the other cats, half of which are 6 months old and three i know for a fact he doesn't like. But then again, going from loner to 12 is a lot for ANYBODY. Which also  might explain why he's so chill about my cats unless they get in his space. That being said, we now have 8 inches of snow freaking overnight and i don't think they'll be outside for a while so I'm not sure what's all going to happen now. I'm getting Badger neutered in a few weeks so I'll defiantly bring Russia's feet up. Oh yeah, AND they (original owners) had him tattooed as well.