Wanted a legal advice on land issue

There was property which registered on name of my grandfather'father' father according to the khatiyan.He was one son.Then he was three son i.e. my grandfather had three brother. Rest of two brothers have no child. My grandfather have two child. My father younger and his big brother. One of my grandfather's brother had registered his will to both of my father and his big brother. Then, rest of one brother had died without registered will to any body. After my grandfather death, my grandmother registered his will to my mother.And father's big brother registered will to my father. He has four sister and a son.His all four sister and a son nortured my father and made marriage to all daughters. After thirty years,my father was died three years ago.He gave some part of our land to big brother' child for living. Now, he is claiming half share on my house property. That is registered on my father and mother name. What is legal right? Please suggest me and my action to solve this matter.