Rules of Court
Section 9. Grounds for disallowing will. - The will shall be disallowed in any of the following cases:
(a) If not executed and attested as required by law;
(b) If the testator was insane, or otherwise mentally incapable to make a will, at the time of its execution;
(c) If it was executed under duress, or the influence of fear, or threats;
(d) If it was procured by undue and improper pressure and influence, on the part of the beneficiary, or of some other person for his benefit;
(e) If the signature of the testator was procured by fraud or trick, and he did not intend that the instrument should be his will at the time of fixing his signature thereto.