According to the symptoms you describe, the cats
need antibiotics. When there is heavy discharge, the best treatment
is antibiotics, like Clavamox would be one. It could be they have feline herpesvirus or feline calicivirus. Feline chlamydia, a bacterial infection, can also result in upper respiratory tract infections. I am going through that with my own cats, sneezing being the only symptom. Clavamox works well at killing the bacteria that causes this type of URI.