So this past Wednesday morning I brought home a 9 year old tabby spayed female. I already have a 2 year old spayed female. The new cat spent 2 days in the room and feedings took place in the room. Friday evening I opened the door and fed the cats in the same room (5 feet apart). There was no aggression from my resident cat and there was some hissing from the new cat but she ate. And after I have been separating them again. So far no issues and I feed them breakfast and dinner in the same room. And we have treat time and pets in the room midday. And there is no issues. However once I shut the door and sit in the living room they "fight" under the door. Each sticking their hands under and hissing and growling. It bothers me because they will eat so close and sot in the room together with me. But if I'm not there they turn on each other. Instantly. And if I come to the door my resident cat quickly stops fighting and lays down.. idk should I keep feeding them in the same room? Should I go backwards and feed them at the opposite sides of the door? Any help is appreciated