If a Question of Mental Capacity Could Arise During a Modification

If a question of mental capacity could arise during a modification of a will, what is the recommended action to maintain the validity of the will?

A) Have a family member sign an addendum to the will attesting to the testator's soundness of mind and body.
B) Have beneficiaries sign a notarized statement declaring the intent to receive an inheritance.
C) Have witnesses sign a notarized statement declaring the testator is acting in full mental capacity.
D) Have the testator sign a notarized statement declaring the beneficiaries' validity to receive the inheritance.