Division of property

My hindu grandfather had 10 acres land which was inherited from ancestors,He died in 2001 .He gave 6 acres land on my grandmother's name who is still alive and rest on my father. My grandfather has 1 elder son who is my father and rest 4 daughters. Now my grand mother has shared the land only among her daughters.Is this lawful. 1. My father is not given share 2.As i heard, what my grandmother did will be valid only if my grand father had bought or earned the land and not as inheritance.Is it true.