Oriental kittens & cats in Marion, Ohio

Mocha is a 4 year old male. Mocha and 2 of his litter mates were abandoned at our home when they were 6 weeks old and we took all three of them in. All 3 cats have lived well together until the past few months. Mocha is a very aggressive male cat and is bullying and attacking the other male cat. We have been working with our vet to try and resolve this issue and have tried for the last 3 months to have the males separated and attempted to reintroduce and that has been unsuccessful. Mocha still taunts and attacks the other male cat to the point that the other male cat is now depressed and will not leave his room. He occasionally attacks the female cat but she does fight back so he backs off. When we allow Mocha out of his room, he is very social and affectionate with my husband and I. Mocha is an indoor cat. I don't know how he would do outdoors. Mocha needs to be in a home without other cats. He is a good pet but should be the only pet.