Aunt's son claiming share in grandfather's property

I belong to Muslim religion. My question is about my grand father's property as he died in 1997 without writing a will. He had two sons and one daughter.After his death my father who is an elder son stayed in rented property without any of property partition. My grand mother told that after her death two sons can divide their fathers property. My father's sister got her part of property while her marriage in 1980.Now my grandmother letting her younger son to occupy the property without any notice to my father. What can we do now for property partition?????