Right of unmarried handicapped daughter in ancestral property

Dear sir, We have a problem with our ancestral land. My grand mother and grand father gifted their ancestral property to their daughter and registered property on their name with out any notice to my father. The person to whom they have gifted the property now she is not alive. And my grandparents are having one elder daughter who is unmarried and mentally handicapped. She was spent her entire life with the parents till they alive after they passed away my father became care taker for her and now she is staying in the same property. My Uncle has filed a case against my father to vacate the property. Till their death my father taken care about my grandparents and given moral support. As he could not give many due to his small salary (worked as watch man). Kindly, help me for below quires: 1) Do we and As a unmarried and mentally handicapped daughter she doesn’t have right to have their parents property?