My Grand father property to grand children

Dear Sir My Grand father bought a house in chennai in 1954, he got three children,( one son and two daughters)first one my maternal uncle, second my mother( With five children), third my mother's sister. my grand father died in 1974 without writting a will., my grandmother was alive living with my maternal uncle in downstars portion, my maternal aunt, after marriage in1971, occupied the first floor of the house for rent, in 1990, my maternal uncle and maternal aunt, told my mother who is not educated, told her that my uncle want give the first floor to my maternal aunt who is second daughter of my grand father, my mother dint object for that, they asked to sing some papers in register office. my maternal uncle died in 1994, leaving his wife with no children for them, my uncle wife was livng in the ground floor, till 2015 august,. now we came to know that my maternal aunt, threatened my uncle wife and got the ground floor propery in her son's name as gift deed in 2008. Now we found that copy of part ion deed 1990,which states that my mother signed in that the she doent have any share. so the entire property now being swallowed by maternal aunt, i.e my mother sister. can you please help me we 5 siblings of my mother climb right on the property in the court of law. is it worth filling a case on my mother sister and his son.