I have 8 cats and sometimes a couple of mine get into it too.

The first suggestion I can make is to take the one peeing to the vet to rule out a Urinary Tract Infection.

Once that has been ruled out, try giving the aggressive one Nature's Remedy (found in any nature food store). It's an all herbal liquid that will calm the cat. There is also Feliway. It is a plug-in aroma therapy for cats. If that doesn't work, you may want to talk to your vet about possible medication for the aggressive one.

I have tried almost ALL of these remedies when my cat Tucker (now named Otto) kept attacking my oldest male Casey (RB, 2002). It finally became apparent that Tucker needed to be an only cat. My friends adopted him and he has been living the life of Riley. It also helped my cat Casey go back to normal. When he was on anti-anxiety meds, he was not himself. He would hide in the closet and sleep all the time. I really didn't like how it changed his personality. That's when I thought it best to rehome Tucker, since I had Casey since he was 5 weeks old.

You should do what is in the cats best interest. Give some of the suggestions a try. If all else fails, find an only cat home for the aggressive one. It might just be the best solution.

Good luck and please keep us posted.