Forcibly and fraudulently Registered Relinquishment deed

We are a muslim family with six sisters and one brother. Our brother fraudulently and forcibly took us to the Registration Office and executed a Registered Relinquishment document in 1987. Our elder sister is not available at that time and she has not signed in the deed. We, 5 sisters signed in the registered document in the Registration Office. Our brother has not paid us a single pie at that time. But in relinquishment deed he mentioned that he paid Rs.5000/- each. He promised us to give the share to the sisters as per muslim law in the property after his marriage. Presently, he sold a part of the ancestral property and transferred the ancestral property in the name of his son. If our elder sister who has not signed in the deed question the validity of the deed? Does the deed become void? Shall we get our shares in the ancestral property?