Oh boy, his feet are really mangled. Poor little guy. Is he using his feet ? Are his front feet the same ?
Can you post close ups of each foot ? Sorry for all the rapid fire questions, just trying to help you out. That is 100% for sure many, many bites. The other dragon views his feet as food....no doubt at all. You must put the healthy dragon in another tank, if you don't have one you can get a large plastic storage tote from Dollar Store/Walmart, Home Depot and rig some lights over it. This is a picture of a simple set up :
https://www.beardeddragon.org/media/30051/full
https://www.beardeddragon.org/media/29889/full
If you like, see if the store will reimburse you for this poor baby [ show them the pics + ask for a manager ] and if you can't set up another home for the other dragon then see if the store will refund you or give it to someone else. Either that or give this one to a rescue. If you're going to keep him you'll need to have him seen by an experienced reptile vet.
>>> vet definitely and immediately.
>>> don't return it to be pet shop, they will most likely take him out the back as soon as you leave , to kill him by giving him the heal of boot treatment , they might even feed him live to a snake !!! 
he deserves better than that ) . This because he is now unsaleable and not worth their expense to give expensive vet treatmet and is his most likely fate in their "tender loving hands").
>>> definitely take the pet shop to task and demand to see the owner and demand help with setting up a new viv and with vet bills BUT THIS IS NOT THE PRIORITY RIGHT NOW & CAN WAIT.
>>> warning his vet treatment is going to be expensive ! and was avoidable , the vet will give you a quote to repair as much as is practical any damage and to treat him ( you are better off doing the post op intensive care at home under vet supervision (giving pain relief and antibiotics, wound care and dressings) as it'll be extremely stressful for him to stay longer than necessary at the animal hospital and they can never give him the time and loving care you and your loved ones can at home.)
Raw unpasteurized honey can be used to fight infection + kill bacteria but if you use it you have to be sure there are no loose crickets in the tank, they would then be attracted to his feet .
Best wishes for your baby.
