ancestral property

Ancestral property is one which confers rights on everyone in the family by birth. But you say your grandfather had already transferred the property to your father, while he was a minor under the guardianship of your grandmother. Hence this property cannot be an ancestral property. You have not stated whether how your grandfather got the property, i mean, whether it was purchased out of his self-earnings or it was devolved from his ancestors. If it was from his ancestors, your grandfather's transfer of the property is not valid, but otherwise, if it was self-acquired, his transfer/settlement to your father is valid and your father got absolute right over the property as absolute owner and he can deal with it freely as per his own wish.