Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online, read about your situation, and wanted to help.
Again I do apologize that my colleagues could not aid you sooner. If you would still like assistance, can you tell me:
How long have they been coughing?
Any eye or nasal discharge? What color?
Any changes to their breathing or fever?
Have you only treated with antibiotics?
When were they last wormed?
Any access to toxins, harmful plants, or heavy metals?