Need help on Ancestral Property Right on NANA House

Dear Sir, My NANA ji has his house in Kanpur-U.P, which was funded from his income only. My NANA ji expired 9-10 years back and there is no WILL for the property. NANA ji has 1 son and 2 sisters and I am the son of eldest sister. 8 years back, NANA ji's son i.e my MAMA got couple of N.O.C documents signed by both the sisters, by cheating, and got the property transferred on his name by completing all related legal formalities with Registrar & Municipal Corporation authority. We came to know about this just 1 week back and when we asked our MAMA ji about this, he simply said, its not his fault at all, as both sisters have signed the papers and raised his hands and said GET OUT to all of us. We also asked our mother, who is now 67 yrs age and her sister, about this, but even they feel helpless and accepts that my MAAM ji cheated both her and the other sister. I would request you to please guide us in letting me know the appropriate action which can be taken from our side against our MAMAji, which not only teaches my MAMA ji a lesson but also get my mother & mausi ji, her justified rights on the property. Looking forward to hear from you on same.