Procedure for reconstruction of ancestral property without permission.

My grandfather died a few months back without any will, leaving behind my grandmother, Two Sister and two brothers. Me & my uncles family stay in Mumbai. We have small house in our home town, my grandmother is still staying there, as she don't want to come to mumbai, we are rebuilding this house. As this house is very old and some of his part started falling. One of my aunt husband is trying threat us that you cannot build this house without my wife signature & her permission. Also he is threat us that he will send us legal notice to stop the work & separate the house Property & agriculture land. We do not want to separate house & land. My grand mother & other aunt has no problem rebuilding this house. Pls. guide for further action.