Is this considered mental illness? Sick?

Hi, My parents send my older brother to a mental hospital many years ago. He stayed there for 1 week, the doctor said that he was not sick and that it was just his character. I saw him talk to himself loudly all the time, and he acted like he was fighting with someone (there was no one there). He also yells at people a lot, mentions things that never happened and accuses me of ruining his life (I never did anything; I was twelve when he went to jail for selling drugs). I'm about to graduate, so I will start looking for a job soon, I'm scared that he's going to hurt my dad when I'm not home. He seemed unstable. (He once tried to throw a giant gallon of water at my mom when they had a fight, and he hit my dad when he tried to stop him etc.) Do you think he is sick? Cause I'm scared that if we send him to the hospital again, they will say they cannot help him because he's not sick? Please help me.