1. Since your grandmother is reported to have died intestate then all her properties except the property that was transferred by a registered gift deed, shall devolve equally on all her children, they shall be entitled for an equal share in the property lying on your grandmother's name.
Your father shall be entitled to half share in the gifted property owing to the relinquishment made by his another sibling in that particular property.
2. Your paternal aunt may not be entitled to any share in the gifted property.
3. He is entitled for a legitimate share in other properties because he has relinquished his rights only in the gifted property and not the other properties
4. Yes, he can.
5. The properties lying on your deceased grandmother's name shall devolve equally on her legal heirs I.e., her own children and the share of her deceased children shall devolve equally on their own legal heirs.
6. The party on whose name the registered sale deed appears can claim the ownership of the property as an absolute owner.
7. Do you have any property on your name?
In a partition suit, your father can include all the properties lying on your grandmother's name.
8. You fight the case on merits with the support of documentary evidences in your favor and win the case.