First, forget the 'must prune or they won't bloom', that doesn't apply to hydrangea.

Annabelle and Incrediball are hydrangea arborescens which blooms on new wood (the current seasons growth) making it possible to prune in Fall, Winter or Spring and still have flowers produced that year. During a young plants first few years though, simply deadhead - remove the spent flower heads by cutting above a strong bud. When the plants have matured, you can reduce in size as needed.

Endless Summer and Forever and Ever Peppermint belong to a group that bloom on both old wood (growth produced the previous year) and new wood (growth produced the current year). This is a trait especially attractive to growers in harsher climates than yours who will often lose flower buds to winter kill or late spring freezes. Again, with your newly planted shrubs, all you may want to do is deadhead - it is not necessary to prune them every year other than to remove anything damaged or shape to a size you find pleasing.