Are they molting? If they feel like they are puffed up and full of liquid, they may have egg yolk peritonitis and ascites. Here are 2 links with info:
https://www.backyardchickens.com/t/68731/laying-hens-with-water-belly-or-ascites
http://www.avianweb.com/eggyolkperitonitis.html
Neomycin will not treat a respiratory disease. You are better off with using oxytetracycline or Tylan. I would separate the rooster and treat him separartely. Antibiotics in your water will get into your eggs, so they will need to be discarded for a certain period. A smear of blood...