Okla. Stat. tit. 43A, § 11-105
A. An advance directive for mental health treatment is valid only if it is signed by the declarant and two capable witnesses eighteen (18) years of age or older. The witnesses shall attest that the declarant:
B. None of the following persons shall be eligible to serve as attorney-in-fact to the signing of an advance directive for mental health treatment:
Added by Laws 1995, HB 1353, c. 251, § 5, eff. November 1, 1995.