Thank you so much @Wyorp Rock
I have contacted my vet. I do not understand the carrier thing. What is the point of quarantine if the chickens are symptomless carriers...your hens would still get ill. Would these infections kill my birds? These new birds are older and it seems they have been living sick for a while. I really do not think it is Coryza, but my vet will help determine that. I did not expect sick chickens. Could it be the air they were breathing in the room they were kept? It was ammonia smelling, I could not even breathe.
Birds that have respiratory illness are generally considered carriers. Some birds may never show symptoms or symptoms may present when under stress (moving to new housing, molting, other illness, etc.). Quarantine allows you to monitor new birds to see if they become symptomatic. While not perfect, it can help you catch anything contagious and then help you make a determination of what is the next best step for your circumstances.
Yes, sometimes new birds (if carriers) won't show symptoms, but when introduced to an existing flock, the "old" birds will become sick. One way to see if this may happen it to use a "canary" method. While new birds are still under quarantine, take a "least favorite" healthy bird from the existing flock and house it with the new ones. Allow up to 14 days to see if the "old" bird gets ill. If it does get ill, then the new birds would be considered carriers of an illness that your flock doesn't have/haven't been exposed to. Then you would need to decide how you want to proceed. Serious breeders would usually cull all (new + the "canary"). It really depends on your chicken keeping goals and what illness you are dealing with.
If you plan on selling/giving away hatching eggs, chicks, started pullets, etc., then careful consideration and research would be in order. You don't want to further spread an illness if you can help it. You need to think about, not only the money spent, but reputation and ethical standpoint of selling/giving away potential carrier/ill birds.
I hope it makes sense(?)
From the symptoms you describe it most likely is not Infectious Coryza, you don't report a rotten/terrible smell coming from the new birds. Mycoplasma is more likely. Usually birds respond fairly well to antibiotic treatment for secondary infection and with supportive care (vitamins, good feed, clean water and properly ventilated housing), they can recover. Even if recovered they still are carriers, so you would need to be prepared to isolated and treat individual birds that become ill. Testing is the only way to know for sure what you are dealing with.
It is possible that if they were housed in an unventilated area prior to you getting them, they could be suffering from ammonia toxicity or something similar. Your vet may be able to help you determine this. Another possibility is they could have respiratory illness that was aggravated by ammonia build up (a stressor).
I'm glad you have contacted your vet. I know this must be hard, you are trying to help give these birds a better life, but you must also think about your current flock as well. Whatever decision you make, after some reading, research and "soul searching" will be the right one.
Please keep us posted. I would be interested in what you find out and wish you the best.
Ammonia Toxicity:
http://www.poultrydvm.com/condition/ammonia-burn
http://www.poultryworld.net/Breeders/Health/2010/10/Harmful-effects-of-ammonia-on-birds-WP008071W/
https://www.merckvetmanual.com/poultry/poisonings/overview-of-poisonings-in-poultry
