Relatives done Forgery registration n changed land on their names

Hi All, Please help me on how to proceed with the below case? I am from Tamil Nadu. My dad bought a land at Bangalore in 1989. It was registered on 2 members(Joint registration). My mom Rukmani and my aunt’s daughter Mageshwari(Mageshwari currently staying in Bangalore). Oly the GP(General Power of attorney) has been registered. The GP has been signed oly by the Land owner. The land owner had a son. At that time land owner's son was not there and his signature also not there in that GP. Mrs.Mageshwari kept that registered GP along with her. Now the problem is that they did some fogeries and registered the land in their names approxi. 7 to 10 years back. They have done 3 registrations. 1st on Mageshwari, Mageshwari's husband and then on Mageshwari's son. While asking for our property they are telling that ” We got a new written GP from owners son and registered”. Also telling that they tored that old registered GP. Now that land owner(father) is no more. Only his son is alive. We don''t even have a xerox copy of that old registered GP which was signed by the owner(father). Is there any way to rescue our land?????? If we file a case on them, shall we get proper solution? Kindly advice me on this. Thank you.