Rights of second wife children over grand mother's property

My father got married to my mother after his first wife has passed away and she has a daughter. My mother has 2 daughters. My grandmother has a property which is acquired on her own(through her job). Now she has passed away without writing any will. My sister (first wife daughter )is asking half of the property saying that as she is first wife daughter she has a right to get half share. Sir pls let me know what are the rights of my father and my sisters.