Can my mother make a claim, after giving up share in property

Hello Sir We have an ancestral property in Kolkata which was originally constructed by grandfather of my mother. That property was inherited by the father (only son) of my mother. My mother has two brothers and probably 20 years eariler she has signed on a document which stated that she dont want any share in the property. She was told that she doesnt have any legal share, and for some formality she need to sign some papers. Since then, my two maternal uncle's have that property. My Question is : 1) Is there any way how that deed of giving up share by my Mother can be cancelled? 2) As a grandson can I make any claim on the property as my mother has already given up her share? Note: My Mom is illiterate.