My sister fell in love with a little male kitten at the place we volunteer at and my parents surprised her by adopting it. Right now they are staying with us as she is home from school for summer, but in two weeks she goes back to her apartment. Fritz has been around other cats his whole life and seems to really enjoy their company so her and her girlfriend decided to bring her girlfriends male cat, Butters, to the apartment too, so Fritz doesn't get lonely. Butters has been raised around cats his whole life and is very cat friendly too. What's the best way to introduce them? The apartment is neutral ground as neither cat has ever been there.