How to cancel a sale deed once registered

My maternal grandfather had 6 children (4 sons &2 daughters). My mother is the second eldest amongst all. Her father and grandfather died before 2002 and there after all the other member apart from the two sisters died in last 5 years. Out of the 4 uncles 2 have done registered release deed in favor of the rest 2, while grandmother has done a registered will in favour of sons in 2002,and 2003. There was a parental house which was jointly owned by her father n grandfather is recently been sold by the family members of these 2 uncles. The basis of execution was a 1990 unregistered will made by my grandfather in favor of 4 sons. Copy of this will is not attached any where, neither the release deed of uncles and will of grand mother make any mention of this will. We believe this will is fraudulently prepared in order to avoid consent of my mother while executing the sale deed. What are the legal remedies available, can v challenge this deed in court or can file a 420 suit.