How to initiate division of fathers property

We are hindu bengali family. My grand father booked a house in his name. After that my grandfather expired and my father paid all the money left and now the property is registered on my fathers name. My father has 2 children me and my sister (married). My sister and her family wants us to sell this house and give them half of the money. My father doesn't want to give her anything out of it due to some reasons. Can he make a will on my name. Does this property be called as ancestral property. And can my sister claim anyrights on it now and godforbid after my father. Please help as they are very greedy. My father doesnt want to give them anything from it. Please tell all the possible solutions. As we dont even have much money i am still studying.