Tylan is one antibiotic that can be used to treat some symptoms.
Chicken diseases are usually airborne and can travel on your clothes from one room to the next. It is almost impossible for a regular backyard chicken keeper to properly quarantine new birds especially if they are not football...
Can you get one of them to a vet tomorrow to get some antibiotics?
Unfortunately vitamins don't fix chicken diseases and it sounds like you just might have brought home a disease.
Which state are you in?
I can give you a direct link to your state lab and they can walk you through how to gather...