Hi
@My sweet Americaunas 
Welcome To BYC
More information and photos would be helpful.
What symptoms are you seeing - coughing, sneezing, watery eyes, mucous, etc.?
How long have they had symptoms?
What treatments have you tried?
Do you have vet care available?
There are many causes of respiratory issues - disease, poor ventilation, molds and sometimes crop or reproductive disorders.
It is best to seek vet care when possible to help you determine the cause of the symptoms your chickens have.
If they have a respiratory disease like Mycoplasma, Coryza, Infectious Bronchitis or ILT, antibiotics may be needed to treat secondary infections. Antibiotics won't cure respiratory disease, birds that are ill and have recovered or those exposed are considered carriers of the disease.
Sulmet is an antibacterial drinking solution that is prescription only. Your vet may prescribe it for treating Infectious Coryza, Fowl Cholera, Coccidiosis, E. Coli or other diseases/conditions as they see fit.
Common poultry diseases:
http://edis.ifas.ufl.edu/ps044
Archived info:
https://www.drugs.com/vet/sulmet-drinking-water-solution-12-5.html