Although we had to stumble on them, we did find two guides to Semana Santa processions in Xela. The first, produced by Pollo Campero, only told what was happening, but didn't show any routes on the map that was included. The other, produced by the municipal government, included a listing of processions and also had a map, stolen from the Xelapages website and edited to remove any reference to Xelapages, except the red square and arrow pointing to in adjacent to Parque Calvario, did show routes.
What amazes us is that the times shown on both schedules seem to have absolutely no basis in fact. It seems that the individuals managing these processions start them when they are ready to do so and couldn't be bothered by any printed schedule. If we had relied on these schedules, we probably wouldn't have seen anything. Instead, pure luck has worked well for us.