3 chickens with bubbly watery eyes and raspy breathing.

Long story short, I have 3 out of my 5 chickens with crusty, oozy, bubbly eyes and clearly having difficulty breathing. I've seen one of them vomit.
Clearly I have sick chickens.
What I'm looking for advise on is what to do. They are separated from the other two, but I'm not going to be surprised if the other two turn out like this too in the next couple days.

I sat with each one with a warm towel to get the crust off their eyes. One had an eye completely shut.

I've been reading many threads on here....can I really just go to TSC and get antibiotics for a chicken?
I know I sound silly......I used to get my vaccinations and penicillin from TSC for my horses.....but chickens?

Yes you really can, I think it is the same antibiotic you used with your horses (but I do not know horses)
The important thing to know is dosage, here is a good thread discussion
https://www.backyardchickens.com/t/393291/dosage-for-duramycin-tetracycline#post_4759916

This could be infectious coryza or mycoplasma (MG.) Do the chickens smell awful around their faces? That can be mre common with coryza. Coryza can be treated with Sulmet or Sulfadimethoxine in the water. MG is better treated with Tylan 50 injectable, Tylan Powder for the water, or Oxytetracycline for the water. All are usually found in the cattle medicine section. These are 2 common respirator diseases, but there are others, and you should close your flock to new birds until this flock dies, or the new birds would become infected. Here is some info:

Infectious Coryza

Synonyms: roup, cold, coryza
Species affected: chickens, pheasants, and guinea fowl. Common in game chicken flocks.
Clinical signs: Swelling around the face, foul smelling, thick, sticky discharge from the nostrils and eyes, labored breathing, and rales (rattles—an abnormal breathing sound) are common clinical signs. The eyelids are irritated and may stick together. The birds may have diarrhea and growing birds may become stunted (see Table 1).
Mortality from coryza is usually low, but infections can decrease egg production and increase the incidence and/or severity of other diseases. Mortality can be as high as 50 percent, but is usually no more than 20 percent. The clinical disease can last from a few days to 2–3 months, depending on the virulence of the pathogen and the existence of other infections such as mycoplasmosis.
Transmission: Coryza is primarily transmitted by direct bird-to-bird contact. This can be from infected birds brought into the flock as well as from birds which recover from the disease which remain carriers of the organism and may shed intermittently throughout their lives. Birds risk exposure at poultry shows, bird swaps, and live-bird sales. Inapparent infected adult birds added into a flock are a common source for outbreaks. Within a flock, inhalation of airborne respiratory droplets, and contamination of feed and/or water are common modes of spread.
Treatment: Water soluble antibiotics or antibacterials can be used. Sulfadimethoxine (Albon , Di-Methox) is the preferred treatment. If it is not available, or not effective, sulfamethazine (Sulfa-Max, SulfaSure), erythromycin (gallimycin), or tetracycline (Aureomycin) can be used as alternative treatments. Sulfa drugs are not FDA approved for pullets older than 14 weeks of age or for commercial layer hens. While antibiotics can be effective in reducing clinical disease, they do not eliminate carrier birds.
Prevention: Good management and sanitation are the best ways to avoid infectious coryza. Most outbreaks occur as a result of mixing flocks. All replacement birds on "coryza-endemic" farms should be vaccinated. The vaccine (Coryza-Vac) is administered subcutaneously (under the skin) on the back of the neck. Each chicken should be vaccinated four times, starting at 5 weeks of age with at least 4 weeks between injections. Vaccinate again at 10 months of age and twice yearly thereafter.

Mycoplasma gallisepticum

Synonyms: MG, chronic respiratory disease (CRD), infectious sinusitis, mycoplasmosis
Species affected: chickens, turkeys, pigeons, ducks, peafowl, and passerine birds.
Clinical signs: Clinical symptoms vary slightly between species. Infected adult chickens may show no outward signs if infection is uncomplicated. However, sticky, serous exudate from nostrils, foamy exudate in eyes, and swollen sinuses can occur, especially in broilers. The air sacs may become infected. Infected birds can develop respiratory rales and sneeze. Affected birds are often stunted and unthrifty (see Table 1).
There are two forms of this disease in the turkey. With the "upper form" the birds have watery eyes and nostrils, the infraorbitals (just below the eye) become swollen, and the exudate becomes caseous and firm. The birds have respiratory rales and show unthriftiness.
With the "lower form", infected turkeys develop airsacculitis. As with chickens, birds can show no outward signs if the infection is uncomplicated. Thus, the condition may go unnoticed until the birds are slaughtered and the typical legions are seen. Birds with airsacculitis are condemned.
MG in chicken embryos can cause dwarfing, airsacculitis, and death.
Transmission: MG can be spread to offspring through the egg. Most commercial breeding flocks, however, are MG-free. Introduction of infected replacement birds can introduce the disease to MG-negative flocks. MG can also be spread by using MG-contaminated equipment.
Treatment: Outbreaks of MG can be controlled with the use of antibiotics. Erythromycin, tylosin, spectinomycin, and lincomycin all exhibit anti-mycoplasma activity and have given good results. Administration of most of these antibiotics can be by feed, water or injection. These are effective in reducing clinical disease. However, birds remain carriers for life.
Prevention: Eradication is the best control of mycoplasma disease. The National Poultry Improvement Plan monitors all participating chicken and turkey breeder flocks.