The following trees and shrubs in our yard are getting scale on their branches: holly, magnolia, abelia, laurel, hydrangea. Will this kill them? Can you recommend someone we could get to spray them?
Spraying will do more harm to parasites of scale than any good it will do to kill scale. The "armor" you are seeing protects the eggs underneath and will repel spray. If you are vigilant you can watch for "crawlers" and spray at that time, as the crawlers are newly hatched scale insects. Many websites will tell you when crawlers are active in your area. When you search Google include your state's name as a search term.
Here's a good overview of scale problems:
as is this one (although it is mainly about California: