Your grand mother can write a new will for her self acquired property or shares allotted to her .In the above mention property she has no power to make a will because she has only life estate in will.If you are not succeeded in proving the will the shares is also allotted to other siblings .The documents purporting to be a Will or a testament must be legal, i.e. in conformity with the law and must be executed by a person legally competent to make it.
A probate means a copy of the Will, certified under the seal of a competent Court with a grant of administration of the estate to the executor of the testator. It is the official evidence of an executor's authority. A probate is mandatory when the Will is executed by a Hindu, Christian or Parsi in the cities of Mumbai, Calcutta or Chennai, or pertains to immovable property situated in Mumbai, Calcutta or Chennai.
Effect of grant of probates : A probate granted by a competent court is conclusive evidence of the validity of a Will until it is revoked and no evidence can be admitted to impeach it except in a proceeding to revoke the probate. However, it only establishes the legal character of the executor and in no way decides the title or even the existence of the property devised. The grant of the probate decides only the genuineness of the Will and the executors right to represent the estate.
The grant of a probate is conclusive evidence of the testamentary capacity of the person who made the Will.
A probate is conclusive as to the genuineness of the Will and appointment of the executors.
Once a probate is granted, no suit will lie for a declaration that the testator was of unsound mind.
Probate is conclusive as to the representative title of the executor.
To whom probates can be granted : Under the Indian Succession Act, 1925, a probate can be granted only to an executor appointed under a Will. However, it cannot be granted to a minor, a person of unsound mind, or to association of individuals, unless it is a company that satisfies the conditions stipulated by the government.
When a probate can be granted : A probate cannot be granted until the expiration of seven days from the date of the testator's death.
Letters of Administration: In the event a person dies intestate or a Will does not name any executor, an application can be filed in the courts of law for grant of probate.