In general, you cannot challenge a will before death.
The primary reason you cannot challenge a will before death is because the testator, at least in theory, can change the will before death. “A will has no effect whatever until the death of the testator and conveys no interest prior thereto.” Johnston v. Scott, 76 Misc. 641, 137 N.Y.S. 243 (Sup. Ct. 1912).
Court have referred to the will of a live person as being “ambulatory,” meaning the testator can change the will before death. As explained in Beadle v. O’Konski-Lewis, 2016-Ohio-4749, 68 N.E.3d 221 (Ct. App.):
However, it is well-settled that [a] will is ambulatory in nature, and until the death of the testator, and until the law admits such instrument to probate, it gives no accrued rights to the potential takers of benefit. Thus, the March 23, 2000 will, even if it is the last valid will, does not create in appellant a “legally protected interest” in Lewis’ property until Lewis dies.
In Beadle, the challenger contended that, because the testator was permanently incompetent, the will was no longer ambulatory. The Court easily dismissed the argument:
Appellant attempts to circumvent this result by creatively arguing that the August 24, 2010 will and trust are no longer on account of Lewis’ irreversible incompetence. * * * Appellant claims that the law contains a well-defined exception where the testator is permanently incompetent that would, in essence, vest him with rights in the property as if Lewis were dead. We find no such exception, nor do we think that it would be good policy to create one. * * * First, such a conclusion does not account for future advances in medicine that, while unfortunately not likely in Lewis’ case, may be able to reverse the effects of mental degeneration. Second, and more importantly, vesting the beneficiary with legal property rights would, among other things, place him or her in a position adverse to the guardian or trustee of the incompetent testator as it relates to the funds expended for the care of the testator, which would undoubtedly incite litigation even in the absence of fraud or some other breach of fiduciary duty by the guardian or trustee.