Dear M'am/Sir

My name is Nakul and I am a respectable citizen of India. My late father was a retired IAS officer and my mother has done law though she has not practiced for the last many years. My parental house is in Luknow and I live in Delhi with my mother and wife. We have some not very well to do relatives who live in our Parental home as caretakers. We visit Lko only once in a year or so. The problem is one of my cousin got married to girl in Lko, the marriage ended up in a divorce a couple of years later. In 2009 the father in law filed a complaint in the local court and included my mother's name as one of the harassers, however I presented my case to the local police there and got my mother's name removed from the list as she had nothing to do with it. Now I have recently got news that the father in law has again launched some sort of a complain in the magistrate court. My question is, is there a way to prevent such harassing false cases ? Do I have enough for a defamation case ? Because I want to get over with this nuisance once and for all. Please help !