Prevent property from getting into litigation

My grandfather (paternal) passed away in a road accident in 1984. He never made a will. He owned an independent house where my grandmother and unmarried physical handicapped aunt lived. My aunt had a private teacher job to take care of her financial needs. Now my grandmother is no more and aunt lost her job recently. My father had 3 brothers and 3 sisters (including my unmarried aunt). As there was no will, I believe everyone has equal share in the house. Now to take care of her financial future my aunt wants to sell the house and share money with everyone. We understood that all the surviving children of my grandfather have to apply for legal heir certificate. As my father passed away recently, I, my brother and mother also consented to apply for it. However, the big problem now is that one of my married elderly aunt is refusing to apply for legal certificate. She is not willing to co-operate in any manner moving forward. She is not understanding that her unmarried sister has no source of income and is in desperate need. In situation like this, 1. How can we sell the house? 2. Can we take any legal action against my un-cooperative aunt as she has made it clear that she wouldn’t sign anywhere. I desperately need a solution to help my unmarried aunt who is now old and needs financial help. This sale can take care of her for rest of her life. Else if we don’t sort this sooner, the house may go into litigation forever. The house has a shared wall with neighboring house and the current owner wants to demolish it thus causing structural damage to this one as well. Hence it becomes absolutely necessary for us to find a solution soon. Again, how we handle if one of the siblings is not co-operating?