Bed and lawn look like it gets wet in that area, heather must have good soil drainage and aeration at all times.

Two on the left don't look fixable, I'm afraid. They're pretty surely dead.

It looks as if the rootballs dried out. Did you score and loosen them a bit? If not the rootballs tend to dry out and shrink which breaks capillary action with the surrounding soil. Almost all of the heaths and heathers I've purchased have been rootbound. Not a problem if you rough up the rootball and water good when planting and never letting them completely dry out thereafter.

One is too close to the lawn.