Boyfriend and Step-Brother sworn enemies..?

My boyfriend called the cops on my step brother. What happened was i suppose my brother was stealing stuff from my boyfriend (KC). But KC has no proof that anything was stolen. I think KC is just trying to get my brother sent away. I am pretty aware that KC doesn't like him. And the only reason he doesn't like him is because my step brother is "in love" with me. It has gotten so bad to where they are having fist fights in the kitchen. And I don't want to kick my brother out of my house, because im the only one who actually cares for him.I have talked to my brother, but he is a 5 year old stuck in a 16 year old's body. KC on the other hand i can't talk any sense into him. He thinks he is always right, and says that because he is 22 he runs everything. Well now my step brother is spending the day in jail, and KC is all giggling and happy. Im kinda annoyed, and honestly don't know how to deal with the situation. I really don't want to though.....Suggestions..?