Claiming ancestral property

Hello sir/madam, My grandfather's self aquired property, a house built by him exists in new delhi. My grandfather had three sons, my father being the youngest. My father left the house after marriage due to family disputes around 38yrs ago in 1977. The other two brothers stayed there and as the second brother was not mentally strong(though he was a govt. servant) the eldest brother got a will made in his name on a plain paper and got it registered. (the will said something like this.... after me all my property goes to my wife and then my eldest son and his family and no legal heir can claim it). Grandfather was around 80yrs when the will was made and died around 1990. there is no probate of the will though. Now my grandfather, grandmother, my father, the eldest son have already died. The eldest son’s wife with her family , and also the second brother and his wife live in that house. My father never claimed the property as somehow he never wanted, and the second son was never thrown out of the house, so he kept living the house but never claimed. Now the eldest son’s family want to sell the house and get the second brother and his wife out tactfully by offering them a very low amount. As the second brother is 80yrs now they are ready to agree with them. And we were never informed because we have been out for 38yrs and not in good relations with the eldest brother’s family. I never claimed the property fearing failure in the case as we were out for many yrs. Now second brother has a daughter who is married and she wants to support me, to claim our shares in the property though her father is not interested because of old age. So finally I want to ask If I can claim my share If the will can be proved invalid :- as there is no probate (if probate is necessary for new delhi) as grandfather was old that time, and that the elder brother just got it signed from him, becos there was no such reason for my grandfather to expel the other two sons from his property. All of them were in good relations at that time. My father and the second brother retired from govt. service of around 40 yrs without any spots on their career. The other brother brothers only have daughters and I am the only male in the whole family at present. Grand father, grand mother, elder brother and my father are no more. Pls advice if there is any hope in the case, and if I should file the case alone or with second brother’s daughter as her father has been living there for more than 50 yrs and if she is eligible to file the case with me as she is married and her father is still alive. Thanks, Regards.