Firstly, you immediately need to talk to your mother about this. She should know about your stepfather’s behavior. Secondly, ask her what you can do in this situation. Unfortunately, you can’t take any legal action against them on the basis of sexual molestation as there is no law for men against sexual molestation in India. But as you said they are threatening you that they will leak your private pictures, then you can file a case against them under cyber law. If any post is harming someone’s reputation in a tangible way. Also, if someone is using someone’s picture without their permission then it is an offense under cyber law. Under cyber law, you can file a complaint in the cyber cell police station against any person who is doing this crime.