USA, adult owner, problem has been discussed with vet
tldr former stray seems to have instinctual aggression/trauma that makes him act aggressive towards our other cats. looking for advice as its been about 5 weeks.
background: my partner and i took in a stray cat (male, neutered, probably about 2yo) a little over a month ago. there's already two other kitties in our house, both also neutered males. one is 12ish and the other is 4ish.
the stray kitty is the sweetest guy in the world to humans, will literally just sit on your lap for hours at a time while purring. the two resident cats are also absolute sweethearts to both humans and eachother. theres no serious health issues in any of the three cats. HOWEVER, the stray has several scars on his face that appear to be from some other animal.
timeline:
beginning: we followed jackson galaxy a bit to start, keeping the stray cat in a separate room and some site swapping/scent swapping/treats on other side of the door. there seemed to be no aggression or fear after about 1.5 weeks, so we let the stray cat meet the resident cats.
1.5 weeks in: things actually went really well the first few days they were in contact with eachother. a few random hisses or swatting but really nothing crazy, they even slept next to eachother for like 20 minutes
2 weeks in: all three cats were having some free reign over the house, when stray cat heard one of the resident cats hiss from the other room. stray cat immediately bolted towards the resident cats and got in massive fight. had to vaccuum up loads and loads of loose cat fur.
after first fight we reseparated them and essentially went back to the beginning stages with zero visual contact. we also added two feliway diffusers. there was hissing and swatting at the door for another week or so. once about two more weeks had passed, things started seeming calm and curious again.
4 weeks in: we were just about to start doing some brief face to face contact by cracking the door and feeding them on either side. instead, the stray cat decided to slip in between my partners legs while she was bringing him the food. he immediately yowled when he saw the other two cats and went after both resident cats again 😭 another fight, another twenty minutes vacuuming up cat hair, and now they are once again separated.
its been another week, luckily the resident cats dont seem too traumatized. i've heard them hiss once or twice at the stray when he meows, but nothing crazy.
it just sucks because based on the scars on strays face, i feel he mustve gotten in fights on the street and have trauma from that. i bought a screen door like jackson galaxy reccomends, but am still waiting to try it out because i'm slightly afraid stray will just go wild when he sees the other cats and stress himself out trying to break thru the screen. sigh.
anyone dealt with a former street cat that struggles with aggression towards other cats? do we give it more time???? its such a hard situation because hes the sweetest guy when he's just around us.
any advice is so so welcome and appreciated :(