Defamation and unauthorized sale of paternal property

My uncle and his whole family has been involved in defaming my father. My father lives in my native village in Begusarai district Bihar. My mother passed away 4 years back. My father takes care of all the agricultural activities on my paternal property. They have spread lies of my father having relationship with maid. Initially they wanted my father to sell a piece of land to get their daughter married but did not want division of property so my father denied. then they started building fake narrative against him. I live outside India but my wife is in native village taking care of my 1 year baby. My Uncle and family has been targeting her as well by spreading rumours , making comments which has badly impacted the mental well being. They have sold a land but their is no documentation and i fear they will create a problem later in division of property. I want to file a case for property sale and also the defamation . Kindly advise