1) your grand mother is absolute owner of said land
2) in the event your grand mother dies intestate ie without a will your father will have only 1/5th share in said land .
3) your uncle 1/5th share will devolve on his wife and children .
4) your grand mother can execute a gift deed in favour of your father wherein she gifts the land out of natural love and affection to your father . have it duly stamped and registered.
5) in the alternative your grand mother can make a will wherein she bequeaths land to your father . will should be attested by 2 witnesses
6) the affidavit executed by your grand mother is not a will . she can during her lifetime execute gift deed or will .
7) for carrying out construction on said land your father would need your grand mother consent