@Eggcessive has give you stellar advice. I would just add here what I would probably do in your situation. It's possible for chicks to recover from a respiratory illness if they have strong immune systems. (That runt chick may be an exception in your brood.)
I would give them Poultry Nutri-drench in their water after dosing each chick with one drop of the drench undiluted. Mix one-quarter teaspoon in a quart of fresh water daily. Do this as their only water source until you see all the symptoms disappear (hopefully). This will strengthen their immune systems so they can better fight off the bacteria. Be aware that once chickens are exposed to a CRD, they likely carry it for life and stress can activate it at any time.
Meanwhile, see if you can talk to a vet about acquiring a prescription for the med
@Eggcessive recommended so you have it ready to go if the symptoms suddenly worsen rather than improve. With chicks, you need to be ready to act quickly or you can lose them.