1) file RTI application as to how sons name is being reflected in property owned by grand mother .
2)once grand mother inherited property by will she would be absolute owner of the land . if grand mother had executed deed of settlement or partition sons would be owner of 8 acres each
3) your father would be absolute owner of 8 acres and you cannot claim any share in said property
4) it is necessary to peruse your grand father will . was it attested by 2 witneses . was your grand father educated ? why was his mark affixed and not signed by him
5) contact a local lawyer . it is difficult to advice without perusing various documents cited by you