If you have several that are sick, it may be easier to separate them for treatment. If you are using Tylan50, then each sick bird will need to be weighed so you give them the proper dosage.
Those that are not sick, I would not treat.
Only treat birds that are sick and showing signs of illness (watery/bubbly eyes, coughing, sneezing, etc.) Antibiotics will not prevent birds from being carriers. If they are all housed together, then everyone has been exposed.
Is this a meat bird?
I would say it's a respiratory disease. Mycoplasma and Infectious Bronchitis are fairly common. The watery/bubbly eyes, I would take a guess it's Mycoplasma, but can't know for sure without testing.
You can try treating with injectable Tylan50 - .20ml per 1pound of weight...