(1) Legal heir certificate issued by government authorities does not have much value. It is good to have it and can be shown as evidence, but by itself It is not decisive. So, please do not give much importance to legal heir certificate. It has limited value. Only a Court order has value.
(2) Usually a partition suit must be filed and the Court hears all the parties and decides who has share in the property. A partition suit has two stages. The Court first passes a preliminary decree of partition and orders who has how much share in the property. Later, a final decree of partition is passed based on the preliminary decree of partition.
(3) You did not write whether your grandmother wrote a will or not. If she did not write a will, you should prove that the will produced by your father is fake.
(4) The law of wills is different in different states of India. In some states, it is not sufficient if a will is written. After the death, the will must be produced in the Court and it must be proven. The two witnesses who signed the will should come to the Court. They should be cross-examined. After hearing all the parties, the Court decides whether the will is fake or genuine and passes an order whether the will is legal and valid. In other states of India, it is sufficient to write a will. No special proof is required. It need not be produced in a Court and a Court order is not necessary. So, you should find out what is the law in your state, whether a Court order is necessary or not.
(5) If your father produces a will in the Court, you must challenge it and say that it is not genuine. Depending on the law in your state, even if it is genuine, it may or may not be valid, if he does not obtain a Court order that the will is legal and valid.
(6) In a partition suit, usually the parties write that they are in joint possession of the property. That is a normal averment in the pleadings. That does not matter much. What matters is whether he has any share in the property as a husband of a daughter. Obviously, you must argue that he has no share in the property as a husband of a daughter. To be sure, you must check relevant judgments of Court and the laws and be fully prepared about this issue.
(7) Joint possession and will are not contradictory. He can claim he is in joint possession and ha can also produce a will. What matters is whether the will is genuine or not. If the will is genuine, he can claim after 33 years also, subject to laws in your state. He can produce the will at the time of evidence. He must also amend the pleadings that your grandmother wrote a will and she gave a share to him. You can oppose when he amends and produces evidence. But even if the Court allows amendments and accepts will in evidence, you can still argue that the will is fake and that he has no share in property as a husband of a daughter. What matters is final judgment passed after hearing all parties.
(8) What you must do is: you must wait till he amends his pleadings and produces evidence at the time of trial. What you must do depends on what he actually does. You must do the following things:
(a) Find out the law of wills in your state. Whether a will is legal and valid without a Court order, or whether a Court order that the will is legal and valid is mandatory.
(b) Obtain all relevant judgments and laws about whether a husband of a daughter has a share in the property or not.
(c) Joint possession does not matter. It is a normal averment in pleadings.
(d) A legal heir certificate is good. You can produce it as evidence and say that your father has no share in property. But by itself, it is not decisive and does not have much value.
(e) You also consult multiple lawyers and discuss the above points and also find out whether the suit can be dismissed right now on the ground that the husband of a daughter has no share in property. Ask the lawyers whether the plaint can be rejected right now under Order 7 Rule 11(d) of CPC as barred by law. That will save you time and money of litigation.
