Bella doesn't pay any attention to them at all. Occasionally Ripley will *play bite* at the air around them and make a silly fake growling sound to try and get them to play or at least react to him. The cats are totally unfazed, especially Trevor who doesn't even bother to look at him. Andy lays there and occasionally bats a paw at him. There are really no problems at all. In my house Trevor and Andy are bonded to each other and Bella and Ripley are bonded to each other. They don't seem to cross those species lines.