(a) If a subscribing witness is also a beneficiary under the will, the witness shall be competent; but the testamentary gift to the witness shall be void unless there are at least two other subscribing witnesses to the will who are not beneficiaries under the will.

(b) An individual may be a witness to a will by which a testamentary gift is given to that individual's spouse, the fact going only to the credibility of the witness.