No, these are not turf "wars." I know as cat mommy and daddy, it is just awful to watch, because you want them to all get along.
But here's our two notable stories of bringing in new ferals.
Every one of our cats is a feral rescue.
Our very first was Lazlo. Only about 10 weeks old. He socialized with us pretty quickly. Skittish still when we brought his brother inside 10 days later. We didn't know what we were doing, and thought they'd be happy to see each other. NOT. Gary handed Shelly in through the door, and I was holding him. He looked up at me - looked around - realized he was not outside - and LAUNCHED himself off my arms and BOLTED. Ran to the front of the RV - nowhere to go. Turn around, ran to the back of the RV - nowhere to go. He kept flying up and down the furniture, all around everywhere - and Lazlo saw a moving target and went for it. They were a rolling ball of fur. Shelly would get away, Lazlo would go after him. There was no screaming - but hissing, little bits of fur flying. We didn't see any blood or anything.... and Shelly found a place to hide, and Lazlo was pooped, so planted himself in the hallway so Sheldon couldn't leave without passing Lazlo.
Meanwhile, Gary's mom was visiting, and we had to get her to the airport. Meant we'd be gone for three hours. Should I go? Should I stay? Well - we decided they wouldn't actually kill each other, so I went. When we got home, we couldn't find them anywhere. I mean - we looked EVERYWHERE. Did they figure out some way to get out of the RV?????????????? The very last place we looked was the crate used to get them to the vet. There they were, asleep, all tangled up in each other. Now - we figured they were fighting, Lazlo chased Shelly in there - and they were just so tired they passed out together.
But that was it. They're not best of friends, but we often found them sleeping together or near each other. Of course, if there was a new cat bed, one would get in, and the other would try to push the other one out - he'd refuse to go, so they'd end up smooshed together in there.
Next story, a bit more appropriate. It is now 7 years later. We have four 7 year old rescues, one that's six years old, and one that's five years old (all feral rescues). A different long story, we had to rescue an almost two-year old boy. We knew he was submissive, but we also knew he was VERY cat friendly, and ours are put up with each other and we have one ambassador kitty, but....
We release Billy into the bedroom and shut the door (we can block off the back from the front of the RV. We left it this way for a couple of hours, but ours are now running at the door to find out who's back here. They've all been told for weeks a new kitty was coming home and just like they were he's homeless, so they'd better just deal with it.
We open the door. Thankfully they didn't all rush in - they came in at various times, and Bill was nervous, but would walk up and try to headbump them. They'd look at him like he was a total alien - and either run away, or bop him on the head, or grab him around the neck, push him down and grab his neck with their mouths. He'd lie down, and that'd be it.
After that, he ventured out into the living room with a fair amount of confidence. He jumped up on the window seat where Tuxedo was. He tried to headbump Tuxie, who looked at him like he was some kind of freak. Billy got down submissively, and backed up - but stayed. He lay down and watched out the window for a while. Lazlo decided he didn't like Billy, and rushed at him. Billy bolted back into the bedroom.
He kept venturing out of the bedroom OK for the first few days... but when Lazlo kept rushing at him, he decided to basically live in the bedroom for the next few months. He'd come out for meals - and we always fed lazlo and Billy next to each other, and that always went just fine.
But at that point, we just focused on getting Lazlo to stop hating Billy. We put Bill scented rags under all the free feeding dishes, we'd play with Lazlo extra and put treats down on a Bill scented rag when we were done. We kept feeding them next to each other, and we'd put Lazlo's food down first. We'd praise Lazlo to high heaven any time Bill came into the room and Lazlo didn't meowl his strange "I don't want him here" meowl (the equivalent of most other kitty's hisses). After a month, when Lazlo continued rushing at Bill, we'd pick up Lazlo, put him in the bathroom, and tell him "you don't have to like Bill, you just have to ignore him" and leave him in there for a five minute time-out. We'd open the door without looking at him and just walk away. He TOTALLY got that we didn't want him rushing at Billy. Billy never gave up. He'd get down on his belly, slowly kind of crawl up to Lazlo in that submissive position, and slowly reach his nose out - and let Lazlo sniff him. Sometimes this worked, other times Lazlo would rush at him or meowl.
We never rewarded Lazlo when he meowled (hiss equivalent) or rushed Bill, but whenever Bill was around and Lazlo basically ignored him, we played with Lazlo, gave him treats, told him what a good boy he was, &etc. It took about 6 months total - and even today (a year and two months later) every once in a while Lazlo will run at Bill - but that's usually if Bill tried to headbump him. And Bill should know by now to just leave Lazlo alone. But our ambassador kitty will often groom Billy these days. Even our Tuxedo - formerly the meanest cat alive - will let Bill headbump him and groom him for a couple of licks on the head - and then bite his near (not hard, just a "I'm done with this"). Flowerbelle (our kitty with the most energy) and Billy play almost every day - a LOT of running around, jumping each other - and we figured out they weren't fighting, because when Billy would jump on her, she'd run away - often fleeing up a cat tree - then poke her head out, look around for him - see him, and run back at him and jump on him. There were no ears back, no ridged backs... there was some crying and hissing, but without the aggressive postures, it's normal kitty play.
So... Horatio may keep coming out to explore, and keep retreating when he gets rebuffed - it may take him a little while to figure out it's better not to try to body rub them. Or he may be like our Bill, and just not give up - but retreat to the basement for longer amounts of time for a few weeks.
Do you have cat trees and a lot of vertical spaces? Window seats for them at several windows? Because the more "up" spaces you have, and the more places you have for them to gaze outside or whatever, the less forced they'll be to have to share the same space upstairs, which may encourage them to develop their own territories upstairs that overlap, but enabling Horatio to have safe upstairs space.
But basically this all sounds very normal to me. They're talking to him in cat language, they're not trying to hurt him. They're working out their language, and Horatio's gonna need a little time to learn it. They don't want to share the territory - but so far they seem not too upset about it - only if he crosses whatever "personal space" line they've got - and then they're not full on tackling him with the intent out for blood - they're using polite cat language to say "get out of my face." Bops on the head, hisses, growls - these are all rather polite ways of saying "leave me alone."
Now... if her ears were back, she was low to the ground, her back was ridged, and her tail was flat/down and waving VERY agitatedly - that is "I'm gonna tackle you and show you no mercy." If it's just hissing/growling, and an agitated tail - that's "I'm warning you." If he ignores that, and walks over - he's gonna get bopped. And he should learn that pretty quickly. If he chooses to ignore it? He should know what's coming.
But really, it doesn't sound like either of them are out for blood. They're just trying to let him know what their boudaries are. Katie could have been a LOT meaner. She was just saying "keep your distance, pal." And by sniffing noses with Bianca, she was saying "Yeah, I don't hate you." But when he tried the full body rub, she said - I might not hate you, but you don't know me well enough to do THAT yet!
...at least that's the way I interpret it.
I'd be very interested to have others' take on it.
And Horatio does look a lot like Jake! Take a look at the picture of my Pinky (top row of cats on the far right next to my nickname at top), and tell me that they are not long lost cousins!! 
