Only way to know what they have is to have one tested.
I also would get a couple of the sickest birds tested. You can't diagnose a chicken and know if it is bronchitis or a mild form of MG by looking at them. If it is infectious bronchitis, they only are carriers for up to a year, but with MG, it will be forever. ILT and coryza are some of the other diseases. Call your state vet or local extension agent about testing. Here is a link for the state vets, and another one for reading about common disease symptoms:
The foamy eyes are a symptom of MG. Every disease, such as IB, MG, ILT, aspergillosis, and coryza may be complicated by a secondary infection, which include those same diseases and E.coli or others. Testing or the easiest thing to do, a necropsy by the state vet on one that dies, is the only way to tell. Good luck, and sorry you are dealing with this.
That's good news!