Forceful land grab by relatives

This is regarding a family property issue. We are a hindu family. My has 2 brothers and 2 sisters. My Nanaji (Mother side) had two brothers and both of them expired long time ago. My nanaji is the youngest of three brothers. The eldest one transferred his land to my Nanaji before his death. The middle brother has a surviving wife. Now both my Mamaji (My mothers brothers) want to transfer the land belonging to wife of middle Nanaji to themselves. They probably will make her sign the papers without her realizing that the land has been taken over. My Mamaji's might achieve this through a will or registration. How can we challenge this forceful land grab? Please advise.