Is your grandfather alive now?
Whether the Will executed by your grandfather in your father's favor came into force as on the date of death of your father.
If yes, then the property belonged to your father and upon his intestate death all his legal heirs, i.e., his children, wife and mother shall be entitled to an equal share in the said intestate property.
Suppose your grandfather was alive as on the date of death of your father, the will executed in his favor will become infructuous and the property will remain on your grandfather alone.