Firstly the property that belonged to your grandmother will not fall under the category of ancestral property .
The ancestral property is always from Male succession.
Moreover your grandmother's property upon her intestate death shall devolve equally on her own legal heirs.
Your deceased father being one of the legal heirs/successors in interest to succeed to the estates left behind by your deceased grandmother, his share of property shall devolve equally on his own legal heirs, that is, you, your mother and your siblings.
You shall be entitled to an equal share out of your deceased father's share in your deceased grandmother's intestate property, your son or none of your own heirs shall be entitled to any share out of your share in the property at least not during your lifetime.