Since the proeprty purchased by your grand father was his self acquired proeprty on his death without any Will all his properties becomes devolved upon his all sons and daughters in equal share.
So the sons along can not divide the land between themselves unless their sisters by a registered deed relinquished their share.
If they did not then on their death their child gets sahre through them and hence they can challenge all the transfers made in the meantime.
So the gift deed done in your favour would be void and ineffective.