Who is Youth Group from Canyons?

Youth Group isn't actually a "who" but a "what". When Brennan's mother begins dating Bill Halverson, Brennan is introduced to the church, as well as the church's youth group, which is run by Bill.

When the youth goup plans a camping trip to the Canyons, Bill invites Brennan and his mother along. Brennan isn't crazy about the group, as they're rather troublesome and violent, so he goes out exploring.... and finds the skull of Coyote Runs.