420 case against aunts

We have a unregistered land of our grand father. Living since my father's age and even further. Father is 65yrs old. Grand father died about 50years back. My father has three sisters and one younger brother.my father is second in the family.Elder sister ,my father and younger brother are married. Two younger sisters of my father are unmarried.we do have a shop too and my aunt's are enjoying it.my grand mother died in 1991 and during her final days she was not allowed to talk to sons or to grand children. I am 33 now. After her death, aunts have cheated us by making a property of my Grand mother and registering it on their own names. Dad is innocent and has no idea of legal things. We have been living in the property and do have water , electric bills,gas bills and tax bills on y father's name. Similarly my aunt's and uncle have their own bills. We do not have any proof of my Grand father's ownership except that he lived there for ages. The property is definitely not bought by my grand mother that she can gift it to daughters. We believe that it's a cheating done by my aunt's to cheat us. Aunts have placed a case in court for their ownership of the house and want us to be vacated.please guide us.