IMO, I would euthanize those birds. If they do have Coryza or some other respiratory disease, then they will be carriers for life and could spread it to the rest of your flock. That's a risk I wouldn't be willing to take. Not only that, but I wouldn't have bought them in the first place. I just hope you are providing good quarantine measures.
I understand that not all of us here are trying to breed these birds. Regardless, it should be the job of any owner of any breed of poultry to improve that breed's prolificacy and health by even the smallest means, whether by culling those with inferior characteristics or simply not letting them procreate. There's nothing wrong with having birds of sentimental value, I have several myself that are hatchery birds that were my very first chickens. But there is a larger picture out there that most people don't see, and that is what we need to strive for.
I understand that not all of us here are trying to breed these birds. Regardless, it should be the job of any owner of any breed of poultry to improve that breed's prolificacy and health by even the smallest means, whether by culling those with inferior characteristics or simply not letting them procreate. There's nothing wrong with having birds of sentimental value, I have several myself that are hatchery birds that were my very first chickens. But there is a larger picture out there that most people don't see, and that is what we need to strive for.