According to the scenario you have mentioned, let me brief you about the grounds on which a Will can be contested.
The will can be contested on seven grounds which are-
Lack of due execution- A valid Will has to be in writing and signed by the testator in the presence of two witnesses, who must also attest to the Will. If the process is not followed, the Will can be challenged in the court of law.
Lack of testamentary intention- A will can be challenged, if it can be proved that the testator had not intended to make a will.
Lack of testamentary capacity- As per the law, only adults can create a will as they possess a testamentary capacity. When a will is challenged on the basis of a person’s lack of testamentary capacity, it often means that the testator was not in a sound state of mind or had a disorder - senility, dementia, or insanity, was under the influence of a substance, or lacked the mental capacity to make a will. A person possessing testamentary capacity will understand the nature and value of his or her assets and the legal effect of signing a will.
Fraud, forgery or undue influence- You can challenge a will by showing that the will was procured by fraud, forgery, or undue influence. This usually involves someone manipulating a vulnerable person into leaving all or much of the property to the manipulator. The term "undue influence" merely means that the person lacked the free will to bargain because of the manipulator.
Lack of knowledge or approval- The knowledge and approval of the testator are naturally presumed when it is known that the testator had the necessary testamentary capacity. However, a will could be contested if it is proved that it was created under suspicious circumstances where the testator was not aware of the contents of the will.
Revocation: Claims by family-. As per law, the head of a family is responsible for the proper maintenance of certain close family members who are specified in the Hindu Succession Act. You can claim in the Family Court or the High Court asking for provision to be made for you out of the estate.
It is advisable to challenge the Will in the court as early as possible to prevent its execution. If the Will, is executed, then it would be termed invalid, and the court would distribute the property as if no will ever exist.
Hope it helps,
Regards,
Srishti