Maybe "The Mission" (PG) with Robert De Niro, Jeremy Irons, and Liam Neesion. Here's 2 summaries from IMDB.com:
Jeremy Irons plays a Spanish Jesuit who goes into the South American wilderness to build a mission in the hope of converting the Indians of the region. Robert DeNiro plays a slave hunter who is converted and joins Irons in his mission. When Spain sells the colony to Portugal, they are forced to defend all they have built against the Portugese aggressors. Written by mattbballman17
Father Gabriel ascends the mountains of Brazil to bring christianity to the natives. He is successful and brings about a golden age among them. Mendoza, a slaver, kills his brother in a fit of rage, and only Fr. Gabriel's guidance prevents his suicide. Gabriel brings Mendoza to work at his mission with the natives, and Mendoza finds peace and asks to become a priest. The church , under pressure, cedes the land to the Portuguese which will allow slavers in again. Mendoza breaks his vows and organizes the natives to resist while Gabriel warns him to help them as a priest.
or "Molokai: The Story of Father Damien" (PG) (IMDB) The true story of the 19th century priest who volunteered to go to the island of Molokai, to console and care for the lepers.
or "Brother Sun, Sister Moon" (about St. Francis of Assisi).
It's been awhile since I've seen these, so it might be worthwhile to preview them to make sure they are appropriate for your audience.