For the following reasons your suit may not be maintainable:
a) Your grandfather's father's property, upon his intestate death shall devolve on his own legal heirs, i.e. your grandfather and his siblings.
Since they are living and the property has not passed on to their next generation, the property is not ancestral to you and it will become the jointly shared property of your grandfather and his siblings.
b) If your father died before the year 2005, i.e., before the latest amendment to HSA took place, then you cannot claim coparcenary rights in the property for a share , including a share out of your father's share in the property, because your father himself was not entitled to any share out of his father's property during his lifetime.
You have filed the suit in the year 2004, hence it may not be maintainable.
c) The sale of property took place subsequently, after instituting the suit, hence it is a subsequent development, therefore at the maximum you can include the subsequent purchasers as party to suit.
Therefore, in my opinion, the suit filed by you may not be maintainable in law.
Dont be under any misguidance and waste your time, money and energy, instead you take a second opinion from another lawyer in local or elsewhere.