What legal action can be taken against parents for threatening?

A son, who was facing financial difficulties, sold his parents’ silver/gold while they were away. It is important to note that his financial difficulties were mainly caused by emotional abuse and defamation by his parents. After they returned, he handed over the sale bill copies to them. This happened about two years ago. Now, due to an ongoing family dispute, the parents are repeatedly threatening to file a theft case against him. What can be done in this situation? He is also being threatened that if he takes legal action against his parents, or mainly against their other son, regarding the current dispute, they may file a complaint against him for those past acts. If they do so, can he seek quashing of the complaint by showing audio/video evidence that it is merely an abuse of the legal process or criminal intimidation to force him to submit to their demands in the present dispute? What is the legal position? Please advise.