We, recently, adopted two cats: Phoenix and Miko. They are 13 and 12, respectively. We already had one, Mia, who is 13, but wanted another cat or two that would spend time in our laps. Mia has hip problems and is overweight, so she is unable to jump up much.

We started with the two new ones in Cat's bedroom to allow them to acclimate. At first, the door was closed, but, eventually, we left the door open and put up child gates to keep them separated from Mia. They spent a week under the bed. We rarely saw them except when they were out before they spotted us. (Of course, at that point, it was immediately back under the bed.)

Eventually, they started getting comfortable with us, allowing us to pat them a bit and starting to be out and ready for dinner when the canned food was served in the evening. We'd been leaving the bedroom door open without the child gates, so they had the opportunity to explore the rest of the house. During this time, there were the occasional cat explosions when one of them would come around the corner of the couch or a chair and find Mia staring at them. Fortunately, all of them were declawed before we adopted them so these explosions usually just ended up being a rendition of the normal hiss/spit/growl song.

Things are progressing. Phoenix is the more adventurous of the two and has come downstairs a few times to visit. Miko doesn't seem to come out of the bedroom as much. We've been keeping Mia in my bedroom at night with the door closed, so, I'm sure that he explores. At dinner time, he does come out to the kitchen to make sure I'm getting their dinner ready.

They still growl/hiss/spit at each other and, in true cat fashion, one or the other backs down first and slowly creeps away, either out of the room (Mia) or under the bed (Miko) or into the bottom of the cat stand (Phoenix). We are hoping that, with time, they will eventually reach some form of detente. I think it will take some time, though.