Succession of property

My grandfather has left a DDA MIG freehold flat. He wrote a will (unregistered) duly signed by 2 witnesses in which after his death property to be transferred in name of his wife, his son & his grandson. His wife also died before his death. Further the will says that in event of his wife’s death before him the property to be transferred to his son & his grandson. My grandfather had 3 daughters & 1 son. 1 daughter died long back she has 3 children.

 Please guide me how to get the property transferred in name of my father & myself.