Burning bush (Euonymus alatus) is prized for its brilliant red fall foliage. However, in some regions it has become an invasive plant. It can also be susceptible to leaf scorch, a problem caused by hot temperatures. It's usually more severe on younger branches. Although you say your plants are getting a lot of water, I wonder whether it's enough. Growing along a foundation exposes them to high temperatures and perhaps soil that dries out quickly. If your roof has an overhang, the soil next to the foundation may be extremely dry. I'd be sure to keep the plants well mulched and use a drip system for watering near their roots.
If the weed-and-feed product you used contains dicamba, it could be leaching into the root zone of your burning bushes and causing the drying. Dicamba is taken up through the roots of plants, so it need not come into direct contact with your shrubs to cause injury. The roots of your burning bushes likely spread 10 feet or more into the lawn. If you do lose your plants, consider replacing them with native plants such as red chokeberry (Aronia arbutifolia) or Virginia sweetspire (Itea virginica). Once established, these shrubs are relatively care-free and should live for many years.