(quarantine)
.this happens and is quite normal with out quarantine practices. Disease and illness spreads very quickly. The weak birds will possibly die and the stronger birds will become resistant. Many people just put birds together and let disease spread. Then treat with drugs and try to stop the flow of the disease. It is sort of like shutting the door after the cows are out.
you have a few things you can do
drug and treat for something you have no idea what it is..or
nothing
I recommend for now...nothing..
Let the birds have fresh air, sunshine, good food and exercises...Let the illness run its course. You have already contaminated your coops and birds. let them become resistant....... try to keep the coop clean.
Read about bio security
If you loose any birds...send two of them off to be tested..then you will know what you have and than you will know what you can do and what you should do.
Purchase Oxine in the mean time.
There is nothing you really can do unless you know what it is..
people online diagnose and treat chickens with out even seeing them is ..a bit scary. Avian Vets with years of experience do not know how to treat chickens sometimes...and too many on line are recommending drugs to treat chickens with out know what is wrong.