Transfer of property after the owner.

There is a property dispute going on. My family has been cheated by my uncle and aunt. Actually there is a home which was on the name of my grand father. He loved me and my father so much. There are three children of my GF - Uncle(Tauji), Aunt(Bua)(she is divorce) and my father. When I was very young my grandmother removed my family from the house. Since she dominating so my uncle and grandfather couldn't say anything. But soon my grandfather started living with us as very bad behaviour was done to him. After the sad demise of my grandfather in an unexpected car accident we all were filled with extreme grief. My father and mother doesn't earn so well. And my Tau&tai are both doctors. My Bua is having a govt job of teacher. Recently when i visited that home to wish my grandmother and bua diwali wishes I came to see the entire house was down and construction was going on to recreate it. Without us knowing my grandmother divided the land in three halves and gave the front to my Bua. We dont have any problem with one half that she is getting but when we sell the back portion it would sell like nothing. It is big land all we want is sell the entire land and give us 1 half of the money. My main question is when that land was in the name of my grandfather then how can my grandmother divide the land according her. Yes she is saying we have done the new registry. But that registry must be invalid since she had no right to do so. After the death of my grandfather all his children are equal owner as there was no will left. Kindly suggest me a way to get through this.