My barberry shrubs are not thriving. They have very tiny leaves and are thin and not filling in as healthy barberry shrubs should.
Have you had the excess heat this summer, as reported in many areas out west?
If your temperatures have been above normal, this certainly will effect and stress your shrubs.
Make sure the soil is receiving enough moisture. Mulching with 3 to 4 inches of hardwood mulch can help keep roots cool and moist.
Planting in an area that has morning sun and afternoon shade is also recommended in warmer climates.
This article will help with care requirements.