Mo. Rev. Stat. § 474.330: Who may witness will — effect of interest in will.

1. Any person competent to be a witness generally in this state may act as attesting witness to a will.

2. No will is invalidated because attested by an interested witness; but any interested witness shall, unless the will is also attested by two disinterested witnesses, forfeit so much of the provisions therein made for him as in the aggregate exceeds in value, as of the date of the testator's death, what he would have received had the testator died intestate.

3. No attesting witness is interested by reason of being a creditor of the estate or because he is named executor in the will or unless the will gives to him some personal and beneficial interest.