Thanks for doing the update. People do searches and may end up using the information on this thread. Come back to it in a few years, and you'll be amazed at how many views it's had.
I suspect coccidiosis, too. Do the drench on the sickest.
In addition to the Corid, it would be very helpful to also give them a sulfa antibiotic. Since you've seen and paid a vet, you should be able to convince her to prescribe the sulfa. There is a bird sulfa that mixes into the Corid water...