Not sure about "ayudante". In English the terms are senior and junior churchwarden.

This is NOT an ordained priest. It is a lay person. The first word that springs to mind in Spanish is sacristán, but there is a difference, and Anglican churches have (or can have) a sacristan as well as one or two churchwardens.

Churchwardens have various duties. They represent the parishioners, collaborate with the incumbent priest and are responsible for looking after the church buildings.

"A churchwarden is a lay official in a parish or congregation of the Anglican Communion, usually working as a part-time volunteer. Holders of these positions are ex officio members of the parish board"
https://en.wikipedia.org/wiki/Churchwarden

The word used in evangelical churches in Spain is capillero:

"Capillero (churchwarden) es el nombre de dos oficiales laicos en cada parroquia de la comunión anglicana, cuyo deber consiste, con la sacristía, en las temporalidades de la iglesia y velar por la provisión del mantenimiento para la ordenada celebración de la adoración pública. En Inglaterra uno es normalmente propuesto por el titular y el otro elegido por los parroquianos; en la Iglesia episcopal protestante ambos (llamados "senior" y "junior") son elegidos por la congregación anualmente."
http://www.iglesiapueblonuevo.es/index.php?codigo=enc_capill...

Collins gives this translation too:
https://www.collinsdictionary.com/dictionary/english-spanish...

On the other hand (in the Anglican church):

"Sacristan
The sacristan is a volunteer who has care for the maintenance and preparation of the altar, altar vessels, candles and other communion consumables."

And the contrast is marked here too. This is a churchwarden writing:

"this placed some stress upon churchwarden’s, sacristan and servers as we all sought to support our visitors and help them adjust to our tradition"
http://www.liverpool.anglican.org/I-became-Church-Warden-dur...