Unable to sell property due to legal heir issue

Our house is a self made property of my father. Father passed away in my childhood and house loan was settled by my mother selling her jewels. My fathers father (grandfather) and mother(grandmother)filed a suit such that they want 1/3 share of the property. Few years later, court dismissed their petition and declared son and wife of deceased only have rights to own the property. After some years, we noticed grand father and grand mother names were also mentioned in the legal heir document. As we were in tragedy we didn't look upon the documents as to take necessary steps to remove their names from legal heir at that time. Now buyer is ready to buy the house and we are in a situation to sell it to meet our financial crisis. They are not in a good term with us and giving troubles in other forms. As per the law, all legal heirs should appear in front of registrar and sign noc to the party buying the property. However, they are not willing to do so and wanting us to suffer. Please let me know the best legal ways to sell our house without their involvement.