If you included a photo, it did not come through.

There's a pretty big contradiction between "all of a sudden" and "started a couple of years ago". In any case, they don't look as if they are dying. The green portions look healthy and without obvious fungal infection or insect damage. You really need someone - county extension service, for example - to take a look. It is possible that a sprinkler system is not delivering enough water to the roots, but that is purely a guess. Azaleas, btw, do not die of old age. There are examples in Japanese temple gardens allegedly 100's of years old.

There was a drought during the time of your posts. The partial die out looks like what happened to mine. They like water.