Don't feel bad. You thought you were doing right by your animals and it's not your fault that the person you trusted to care for them failed you and your critters. The outcome may have been the same if you'd sold them.
If all of the snakes are regurgitating then either there's a problem with them all being too cold, or they all have been infested with some sort of parasite. I would have fecals done on all of them, and in addition to the typical roundworms/flatworms/pinworms/etc. I would have them tested for crypto. If they are clean then bringing them back should be a matter of providing heat and very small, widely spaced out meals dusted with a bit of NutriBAC to get their digestive systems back on track.
Your vet may have to stitch up the one that was attacked, so it'll just be a matter of keeping the wound clean, applying a topical antimicrobial such as Silvadene or Vetericyn, and administering an injected antibiotic every few days to ward off infection.