File case against abusive son.

Good day everyone, This is regarding one of my cousin.. He is leaving in Mumbai with his father. Since last couple of years he is not behaving normal. Always harassing his father and asking for money and this habit is increasing month by month and now its everyday. His father is jobless and he is not able to walk or stand properly. My cousin is harassing him and abusing him and sometimes pushing him and bitting him. I think my cousin is taking some medicine or I don’t know what but there is something wrong with him no control. Now the situation is getting more worse. My cousin is working but he is not going for work . In a month 7-10 days he is taking off or not going. His father is really frustrated and don’t know what to do now. My cousin mother also passed away last year because of his behavior and now his father is not in a condition to go anywhere or do something. His father don’t want his son to stay with him. Kindly advise what has to be done in this case and how to file a case against my cousin. How the things will be normalized. Thanks & Regards