Threatening

Lodge police complaint against your BIL in police station of your area and police officer will mention concerned section and you don't worry about it. 

If it is a fact then you should take proper legal action against him by lodging a police complaiont for such act, however what is the reason that he threatens you?

The police file FIR with appropriate sections of law based on the contents of your complaint

the section of law depends upon totality of facts which you  have not shared.