Will my mother be legal heir of ancestral property after fathers death

My father used to send money to my grandfather through money order to purchase a house in 1979 at kerala. House was purchased in the name of my grandfather. He passed away and house was transfered to my grandmother. Grand mother wrote an unregistered will stating my father will be the beneficiary after her death. Unfortunately my father died and grandmother is still alive. Will my mother become a legal hire automatically and instead of my father my mother will get the house after my grandmother's death?