gifted property

Who was the guardian of the child when it was minor, who accepted the gift on behalf of the minor?

Guardian was his father

Gift deed executed by grand father in favour of grand child allowing his two sons to use land but not to sale the land and after demise of his two sons the grand child has all rights regarding the land .and this gifting of property is not known to one of his son. so now he is demanding his share of land now itself ,so grand father want to give his share .so now the grand child want to revoke the gift deed . please suggest the cancellation procedure for gift deed.

Is signature of grand child is sufficient to revoke gift deed as he is major now???