Clarification on gift deed made by grandmother

Hello, My Grandfather had a property of 2acres. Post his death, the property is transferred to my grandmother. My grandmother has 2 sons. The younger son had made a gift deed from my grandmother forcefully without her and elder sons consent and knowledge & got the property registered in his name. Now, both my grandmother and her elder son(we are children of elder son) both are not alive. But we being the children of elder son, can we question the share of my father in the court of law in that property of my grandma. 1. Since, my father's brother(younger son of my grandma) has got the gift deed done from my grandmother, can the gift deed be revoked at any circumstance in the court of law. 2. Does grandchildren have rights to question the share of their father, as the property is currently in the name of my fathers brother. Please share your valuable feedback.