So recently we took in an older family pet - a 5 year old cat, named Spartapuss. He couldn't live with my parents any longer, so he came to live with me and my fiancé in our flat. He was essentially my cat for 3 years and when I moved out we decided not to upset the balance he had with our other family cat, so left him behind. He moved on Saturday and he seems to be adjusting well so far.
The only issue is that we have two 1 year old cats, a boy named Drogo and a girl named Khaleesi. Both are outdoor cats and we fitted a cat flap so they come and go as they please.
Neither has taken well to Spartapuss invading their territory, understandable. For this reason, we set up a safe area for them in the spare room, where they spend most of their time - and Spartapuss has his area in our bedroom for now. We've let them get small glimpses of each other (apart from Drogo and Spartapuss' first meeting which happened unexpectedly, lots of sniffing and curiosity before the defence mechanisms kicked in). We open and close the safe spaces to allow time for each one to roam the flat and get used to the scent of the others regularly. Rotating every few hours, provided the kittens aren't outside.
Drogo has no real issue with Spartapuss, they can be in the same room and, bar from some small confrontation, they generally leave each other alone or just avoid each other. However, our girl Khaleesi - every time Spartapuss see's her, he moves towards her and she runs a mile. It's unusual behaviour from him, especially given how passive he is towards Drogo and having lived in a multi-cat household before.
We want to let him out to roam as he is an outdoor cat, but we're terrified he'll scare away Khaleesi so she won't come back, or otherwise hurt her. There's only one door (our own private front door that leads directly outside) so they are guaranteed to meet and we're worried that if he scares her away from the house entrance, she won't want to come back.
Any advice would be welcome.