Unregistered will

It all depends on the evidence.

A will can be execute even on a plane paper and it requires no stamp paper and no registration.Will should be signed by testator and two witnesses. If beneficiary and other witnesses identify the signature of  testator then will would be deemed proved.

In India, a will does not have to be registered to be valid. What matters is that it was signed by the person making the will (your grandfather) and attested by at least two witnesses. The law also requires that at least one of those witnesses should confirm in court that the will was properly signed and attested. Since your grandfather’s will has three witnesses, even if one of them has turned hostile, the other witnesses can still prove the will. The court only needs one reliable attesting witness to accept the will as valid, provided there is no sign of fraud, undue influence, or any other suspicious circumstances. So, the case will not automatically fail just because one witness has gone against it.

To know further connect with me at adv.vishesh@icloud.com

If an attesting witness to a will turns hostile in court, the propounder of the will can still prove its execution by presenting other evidence, including the testimony of the other attesting witness (if available) or other evidence relevant to the execution. The court will then consider all evidence, including the hostile witness's testimony (if any), and determine if the will's execution has been proven. 

Section 68 of Indian evidence act requires that at least one attesting witness must be called to prove the execution of a will if the witness is available.