The basking spot for your dragons is too cold. Dragons need the basking spot temperature of 105-110 to properly digest their food, as they must raise their temperature to 100.
Walnut shells are a horrible substrate to use, because if swallowed, they can cut the insides of the bearded dragon, even though they may feel safe to run your fingers over them in your hand. They cause impaction, and most likely death.
Even a bare tank bottom is better then that substrate.
I recommend non-adhesive shelf liner.
Also, please read this caresheet about caring for your dragons, it is the newest and best information out there:
http://www.kakadudragons.com/caresheet/