Rights for grandchildren

My grandfather bought a house in 1939, he didn’t do any will. His 3 children, ie; 2 sons and a daughter (ie; my mother). 1. First son, married (died 2007) and 7 children. Wife also died 2004. 2. Second son NOT MARRIED ( died 2004). 3. Third daughter, married (ie; my mother) still alive aged above 79 years and have 4 children. My mother was asking her first brother for the share after her marriage but nothing happened. This first brother mortgaged this property several times in between 1939 to 1970 (staying in the house) for his needs in which my mother has signed in the mortgage deed (my mother’s name appears in all the mortgage agreement). Till 2003 property was in the name of my grandfather and tax is paid in my grandfather’s name, after that till now in the name of first son’s name Meanwhile, my cousins tried to sell this property without my mother’s knowledge to more than 25 people, but in vain. Now in 2014 they tried to contact us in a cunning way saying that “they are going to take a loan and that they want a signature from my mother in a NOC”. My mother said “tell them to give my share, I will sign it”, for which they didn’t agree and we have filed a case. Now they are telling that my mother has lost her rights in the year 1956 itself, which is false. My mother and 2 brothers has signed a mortgage agreement and redeemed back in 1970. My mother did not receive any money till the death of my mother’s brother and after that too. Now my question is:- 1. If my mother is lost her right, why do they need signature now? 2. How to prove that the agreement signed by my mother and 2 brothers is for mortgage and not for sale agreement. 3. Is there rights for the grandchildren to fight for the share. (ie; daughter’s children) I, Suzan would request you to clarify with any suggestion. Property is in Bangalore.