Harassment by daughter in law

Actually our son had married in 2013. Since the day of marriage our daughter in law who was working in some private firms first started quarreling with my son on this pretix or that such as why some lady from office is talking to him and like that. obviously he became furious when we started to make her understand that he is not like this she was adamant to her stand. In between we received three unanimous letters in the name of my daughter in name, which shows that somebody loves her and he is hellbent to get her. Only two letters we could saved and one was destroyed by her herself. For this she said that it is also a trick of our relatives. Then she started to fight on every occasion on every festival. She even developed rivalry with my daughter who is married and tried to almost ban her entry into my house. Gradually she started secretly complaining to my son against us and he started to fight with us. She even threatened to complaint in the police. She does not do any house hold work. All the work is being done by my wife. she always shuts her room. Now she has become a mother of one daughter. But her behavior towards us is very bad. She creates a scene daily and never gets up in the morning upto 10 Ó'clock. She has left the job during the pregnancy. What should we do. Although The flat is allotted to me from the Government but I feel that I myself should not live in that house. - kindly suggest some remedy.