Father died while back do we have share on grandfather's property

Sir, My grandparents house is a 60 gaj house in Tilak Nagar, West Delhi. My father died in July,2000. He had one brother and 2 sisters. My grand parents did not registered their property and not even made their will. They died before my father. We are two sisters only and my uncle has a son. I want to ask if my mother has any legal right on the property and how can she obtain it as patta of my grandparents name is with my uncle.what can he do with it. Kindly suggest asap. Because my uncle and his son are torturing my mother so that she ran away and they have full right on the property.