1. By mere NOC the share of your father and his siblings does not relinquish so as to make your grand mother absolute owner.
2. Only by way of registered deed of gift or relinquishment one's share in the property can be given to another.
3. If by this method your grand mother became its owner then you can not restrain her from transferring the property to anyone she chooses.
4. However the NOC was a mere paper writing then you r your father file a suit for partition to claim your respective share.