My uncle did not

My father bought a house in 1971 in Mumbai as a family home for the joint family between him and his 2 brothers (uncle1 and uncle2). The house was registered in my fathers name but equally owned by all 3 brothers. They also built another house which was registered in uncle1 name. In 1990, my uncle2 wanted the Mumbai house to be registered in his name and so under duress my father had to share out the family properties and signed the Mumbai house to my uncle2 with the understanding he would give my dad 1/3 of the value of the house. My dad passed away within 2-3 weeks . My uncle2 got my mum (who cannot speak or read English) to sign a doucunent which I think was no objection without the knowledge of my fathers children and got the house transferred to his wife's name. When my uncle1 children sold the other property, my mom asked for her share to my uncle 2 and he told her there is no share and he owes her nothing. My mother died 2 years ago. Uncle1 has passed away as well. Now my uncle2 wants his share of the ancestral land and wants my brothers to sign the documents. As children , we want to challenge our uncle for my parents share in the Mumbai house but we do not have any documents nor do we know what papers my parents signed. Do we have a case here?