Q.Orange Rocket Barberry
We bought two gorgeous barberries to go on either side of our front door. Because we don’t plan to stay in our current home for long, we put them in pots rather than the ground. We’ve had some very hot weather and no rain for about a week (temps over 85) and the bushes were in full sun. I was watering them about once a day in the evening, but they have started to struggle. The leaves are curling up, and a lot of the leaves around the base of the plant are dead. I have been guilty of over watering plants before, and I’m not sure if I’ve over watered or under watered. They’ve only been planted about a week. They looked great until about two days ago. What can I do to bring them back?

More water!
New plants in containers will need daily watering, and most likely twice a day during hot weather.
Keep the soil evenly moist, but never soggy. Make sure the pot has adequate drainage holes.
https://www.gardeningknowhow.com/special/containers/container-plant-watering.htm