Any sores must be addressed by a vet. Cat wounds can infect and abcess quite easily and your vet should be consulted to help care for the wounds. I have seen some nasty abcesses in cats from being bitten by other cats and most often they develop because owners just wash the wound off but teh way the cat teeth and nails are, they act almost as if they were needles and often there is bacteria at the bottom of the wound that leads to infection. A vet can help properly flush the wound. As for them not getting along. Well if they are fighting this seriously, it may not be a bad idea to talk to a behaviorist and get a home consult done. In severe cases, it may be wise to rehome a cat. In less severe cases, separation and gradual reintroduction may be the key – and this may take weeks of months to acheive. Other issues with aggression is that one may stop using a litter box – and this can be a tough thing to stop. Is there a vet school in your state you can call or a college with an animal sciences department that may have a behaviorist you could talk to? This would be my first step after having the injured cat checked out by your vet and separating him completely from the other two cats. I also want you to contact Tufts University. Dr. Nicholas Dodman (highly respected) works there and may be able to speak with you on this. He is HIGHLY respected in his field and this issue sounds serious enough to refer to one of the best. http://www.tufts.edu/vet/petinfo/index.html