I've got two 5 month kittens, the runt a black female named Basil and a mainecoon striped male named Milwaukee who's pretty big. They seem to like each other and I'm pretty sure they're from the same litter, although when they were all still outside I never saw any kittens play with basil. I picked her from outside first because she wasn't doing well, the others we relocated later and that's when I decided to keep Milwaukee he's sweet and like human attention. I introduced them slowly feeding them on different sides of the same door they started pawing at each other under the door so I thought that was good and then I let them meet face to face he seemed scared of her and didn't interact much beyond a quick nose touch and sniffs then after a few days they started wrestling basil hisses at him and he'll stop for a second and then try again. I haven't seen any fluffed up tails and basil hasn't tryed to escape him but I am a bit worried, they're always supervised when they interact so I can make sure they don't hurt each other though.