Need help in combating a complex situation

Hello, Coming straight to the point , this is the scenario that we are facing : Year : 1959-1960 ----------------------- 1. My Grandfather inherited a certain 'x' acres of land. 2. He had mortgaged 1 acre of this land in lieu of Rs.2000 from Mr.Y. 3. It is said that he had returned the borrowed money , but did not take back the legal documents. (We do not have any documents presently.) Year : 2001 ---------------- 1. This particular 'x' acre of land is divided into 5 parts among my father , uncles and paternal aunt. One of my uncle and paternal aunt were given the existing house as a share, rest all were barren land. 2. Everybody has mutated the property and houses were built. 3. The mutation did not happen for one of my uncle and paternal aunt sharing the existing house. Year : 2016 ---------------- 1. Both my grandfather and the person from whom he borrowed (Mr. Y) has passed away. 2. Y's children suddenly recovers the old document. 3. They find out that some tax is pending on our old house owned by my uncle and paternal aunt. 4. They pay a certain amount and list their names on the property. 5. Now they claim that they own 1 acre of land . 6. The witness who signed the mortgage deal is still alive and is thought to have provoked this situation. 7. Y's children has bribed the only lawyer that we had decided. Now we are looking upto a new lawyer. Kindly suggest what should be our approach in defending our situation. We are from a low middle class family without any other asset , while Y's children are rich.