What can be done in this property matter

My grandparents Have 2 sons. My father and his younger brother. My father died 26 years ago. My grandfather acquired most of his property on his own name Me and my sister we live and work abroad. Since my father died very early when we were kids my uncle took charge of all legal works with our wishes. Gradually, he took advantage of us being minor took my mothers signature from all the property she has on her name & get motation done . He mislead me and my sister and took our agreement with out our knowledge on a papers saying we(my mother, sister and me) do not want anything from grandfathers assets And the whole property which includes house & other property on his name know post my wedding of 5 year when i am asking my right of property Upon asking for papers he threatens us that do whatever you can do I will not give you a single pany out of this property my mother is a longtime widow , . We trusted our uncle blindly and in return he cheated us big time.We are getting a rent of 1lac/ month from same property but he is not giving us anything to use form it we any legal advice is highly appreciated.