My brother physically abuse my parents

My father disowned my brother from his will because he is an alcholic and abused my parents. He does not even live with them anymore. He got married to someone without their consent. Now when his wife got pregnant he has been taking her to my parents' home to let her meet them. Thursday he dropped her there and left for work. Then in the evening he called and said I am busy so keep her there. My parents did, but at night he came and knocked their door. He was drunk. As my dad opened the door he held his neck and started beating him. As my mom heard the screaming she came and tried to help but he hit her too. Then in 5 mins the neighbors came to help my parents. Someone called the police but till that time he and his wife left. When the police reached they said we are not able to do anything now, so tomorrow come to the police station and give a complaint. Guide me, what to do so my parents can get justice against this domestic violence. They live there alone because I am in US for work