What temp is your brooder?I figured vitamins were a no, I know I couldn't give them nutridrench but it's been two years since I dealt with this so I'm scrambling for information.
Yes it was My Pet Chicken, I've gotten every chick I've raised from them, three broods total including these babies and have had nothing but good experiences thus far. After seeing the three deceased chicks I don't know if I'll ever get up the nerve to order birds online again, it's so stressful waiting for them to arrive and losing three of them was jarring. I'll be emailing them some time soon.
I can call my reptile vet, I haven't gone to them in years but they should remember me, they had some interesting experiences treating my rescue lizards. They might be willing to run a test, I used to get fecal floats done every six months, but they can be pricey since they were exotics, maybe it'll be less for a chick. I'll call anyway, I can use whatever money I get from my refund to pay.
Anything else I can do for the chicks in the meantime? If I remember correctly corid treatment is five days, I have them in a quiet room in the house and am paying extra attention to the brooder temperatures. They get fresh wet feed every hour or so, they won't eat dry feed for some reason. I'm keeping a close eye on their droppings but haven't seen anything weird since the cecal core/mystery mass last night.