Can we assume that you've placed them in a suitable location (sun and soil-wise)?

New plantings require regular watering, especially small container grown plants. It's essential that we concentrate most of that water right on the root ball so that no area within that zone becomes so dry that it repels water. Roots begin to die pretty fast if the root ball dries out for days on end. As long as you've planted in a soil that drains properly, I would not hesitate to water small, new plant every single day until it begins to cool off.

Lots of mistakes can be made when watering. We can set the irrigation system for 10 minutes twice a week and assume that that will do the job. It won't....not for anything.

If we've applied a nice layer of mulch as is correct, we may have piled it too close to the main stem and/or have applied too much mulch. It takes quite a bit of water to finally get all the way through a layer of mulch....even a nice little rain shower may end with the soil under mulch completely dry. Something to think about.

Only you can be the judge about how badly your plants have been damaged, or even if lack of water has been the problem! If it is a water problem, then it is very possible for plants to recover. As a matter of fact, they will WANT to recover, as soon as they can. Dead and damaged foliage can be replaced by new, healthy leaves. If the damage has been so significant to cause twig and branch die-back, then you'll end up doing some major pruning.

Do NOT fertilize your plants, because you don't want to encourage a big flush of growth at this time of year. Simply begin to water them thoroughly. If you haven't prodded around in the soil and around the root ball with your fingers and a trowel, you should probably do so.

Those are my thoughts; I'm sure you'll get helpful advice from others, too.