Granddaughters rights is grand mother property

Dear sir, My case is we are two sisters living in Hyderabad and coming to issue my grandmother has property on her name and she has 3 sons and 2 daughters and they have got their own houses in given by our grandfather to their children’s and one of her son is my father and he had deceased when we are kids and our mother became mentally disabled and by this this my grandmother took advantage and wrote her name on our fathers share property and she gave education to us and brought up and now we are married. What is the procedure for getting that property from grandmother she says I will write on our mother names who is mentally disabled but not on our names . Second point is house documents are with us grandmother is forcing us to give her documents and we are afraid of giving docs to her. We have no one support from ur uncles and aunties because they got share houses in different places and living happily only we both are fighting for that property from our grandmother. Give us the solution to get that property but in colony everyone knows that property belongs to us but my grandmother playing games with us since we have no one support please guide me .