A power of attorney is legally sufficient if all of the following requirements are satisfied:
(a) The power of attorney contains the date of its execution.
(b) The power of attorney is signed either (1) by the principal or (2) in the principal’s name by another adult in the principal’s presence and at the principal’s direction.
(c) The power of attorney is either (1) acknowledged before a notary public or (2) signed by at least two witnesses who satisfy the requirements of Section 4122.