How to claim on maternal grandfathers property, if my mother is mentally challenged and Divorced

My maternal grandfather was government employ and died without any will.He has 2 sons and 3 daughters. My mother is mentally sick and lived at father's home with her brother after being separated from my father because of his second marriage . I have fear that my mother's brother will try to take her share or might try to take signs on some agreements. Or try to sell the property without my acknowledgement, as I too have lived in the maternals home since childhood and their behaviour towards distribution is doubtful and now I have to live outstation for job purpose. As my mother is mentally sick and of ill health. So she lived with my maternal uncle. Kindly tell me the precautionary measures to do, so that I can have her share after her death. And also the required documents for claiming her share. What if my materal uncles will not agree to give me the share or to make the property transfer to their name or to sell? I don't want to share the property with my father because there was separation case filed by my maternal grandfather on my father because he married twice. Also tell me what If my mother dies, how can I get her share. And also the required documents for the claim. Right now I don't want my mother to be in trouble, as she lives at her fathers home,so I can't claim till her death. But I want to make her share safe for myself, as I know she is not well and might get manipulated.