They tend to co-exist, mostly. On a rare occasion they snuggle in the same vicinity, but most of the time they prefer to stay in different rooms. Sometimes they make-out-fight to varying degrees of violence. If I have the window open, they fight for who gets the choice spot, and that can get pretty intense. The other night they kept me up almost all night -- Roy defending his right to the window with yowls and Rupert protesting not being let up my meowing constantly (he's a talker). They both feign non-interest in dominance, but when it comes down to it, Roy wants to be in charge, and therefore loses every time.