Dispute between siblings for family house

3 houses. 1st on is our parental home in our village. 2nd. home is in the name of my brother. 3rd. Home is in the name of my mother. 2nd and 3rd home are in cities. My father died few years back. But in his presence he made a "WILL" with his wife(my mother) that the 3rd home will be transferred to my another son. As of now, my brother is acclaiming that he is also the half owner of 3rd home as it is in our mother's name but just because our father died and the home is in mother's name, he is claiming so. I just have the "WILL" with me which was made in the presence on my father. My mother also doesn't want to right the house in either of the son's name. But my brother is trying to be the half owner of this house. What if she writes the house in his name? What can i do now?