Presuming this is Rhaphiolepis, could be anything with the info presented, but they don't thrive in that position and need more sun. So they are weak already and susceptible to whatever pathogen is there waiting for an opportunity to attack stressed and weakened plants. The remedy would be to plant them in a place with more sun and replace with a more suitable plant.

Dan

As soon as you notice one of the branches dieing (after making reasonably sure it really is dieing), remove the entire branch, bag it in a large plastic trash bag, and take it to your local extension agent. Asked them to try to ID the problem. I don't know what the problem is, but I'd bet, if the branches and shrubs are dieing that fast there will be clues on close inspection.

Indian Hawthorn is susceptible to Fire Blight.

And numerous other banes. If the spot and climate is just right, they can make impressive specimens. Otherwise...