State law prescribes who may perform marriage ceremonies. RCW 26.04.050 is as follows:

The following named officers and persons, active or retired, are hereby authorized to solemnize marriages, to wit: Justices of the supreme court, judges of the court of appeals, judges of the superior courts, supreme court commissioners, court of appeals commissioners, superior court commissioners, any regularly licensed or ordained minister or any priest of any church or religious denomination, and judges of courts of limited jurisdiction as defined in RCW 3.02.010.

Washington State does not license ministers, this is a function of the religious affiliation.

Ministers from any state may perform ceremonies.

The bride and groom may not perform their own ceremony.