Grandparents property - no will - not divided equally.

My grandfather has 4 sons & 4 daughters. I am the son of his 3rd daughter. There were 2 acres of land and an own house in my grandfather's name and 3 acres land on my grandmother's name. His 4th son has been living in the property from last 20 years and he was taking care of both grandfather and grandmother. Also he had the benefits of my grand-parents land including lease amount during these 20 years. My grandfather had passed away 18 years ago, and my grandmother passed away last month. There is no will prepared by my grandfather or grandmother. Until now, the property was not divided between his legal heirs. Now, his 4th son is trying to obtain the entire property. He is saying that 4 acres of land out of 5 was transferred to his son & daughter's name by my grand-parents. 1. If property is transferred this way, isn't a NOC required from all other legal heirs? 2. Is there any law that proclaims that such property with no will should be shared equally to all legal heirs only and cannot be transferred to an individual heir or his family alone without consent from other legal heirs? 3. How do the other legal heirs claim the property (including the transferred land) and the lease amount from last 20 years?