As you can see from some of the examples below, there is not one simple way to translate priosteres. So, I think that you ought to keep the original term in italics with a brief explanation in parentheses.

During the feast, kinship ties between family members are restated and ties with .... In the past, the festival had several sponsors (priostes) and feasting ...
links.jstor.org/sici?sici=0014-1828(199524)34%3A1%3C75%3ADPAPLA%3E2.0.CO%3B2-H

The cacique did not rule directly, but appointed indigenous alcaldes, or mayors, ... The alcaldes, in turn, appointed the priostes (captains) in each annex. ...
books.google.com/books?isbn=0415935288

Diriomeños who titled themselves priostes y mayordomos indígenas, or officeholders in the indigenous community, wrote to the jefe político in Granada. ...
muse.jhu.edu/journals/hispanic_american_historical_review/v083/83.3dore.html

He referred me to one of the nine priostes, a position somewhere between priest and presiding officer, who gave me permission and explained the festival.
http://judylumb.com/deerdance.html

For Filigrés, it means a parishioners, but one who is participating in the rite, so perhaps participants would work, too.