Purchased uncompleted house from sc caste people who want it back

My father purchased a uncompleted house from an sc caste people which was given by government to that person in 1990s by agreement only my father 3 years before sold to my aunt by registration at that time of registration my father submitted current bill demand notice and municipality water tax, home tax reciept as residential proof that it is in our hand from 1993 now they r demanding to handover my house to them my father and seller who sold that uncompleted house are here am I fight for justice