Something I thought of, maybe it's really stupid, but hear me out.
Would it be possible, not necessarily just in a pet store situation but in general, to help ball pythons feel more secure if a person were to use tinted film to cover part of the tank ?
My thought is, it would allow for a little more security for the snake while still allowing people on the outside to see it. I don't know it's probably a dumb idea but still.
I do agree you should do what you can within your limited means to help these guys. Do try upping the food size, even if they are thin as long as you don't go overboard they should do just fine. Try hopper mice or if you can fuzzy rats. If they refuse F/T, try and get permission to do live with supervision just until they start eating again.
I wish you all the best.
Gale