I would get a blood test from the vet to determine what they have. Tylan doesn't treat everything, unfortunately... And giving antibiotics that will be ineffective isn't the best idea.
Short of that, isolate the drippy, lethargic chickens away from the rest of the flock IMMEDIATELY.
Sores under her eyes? Could you post a picture of this? It could be injury, Fowl pox, or bug bites.
Do the ones with eye stuff have a bad smell around their heads?
If you suspect mycoplasma, there are things you should consider: A chicken that pulls through mycoplasma is a carrier for life and can infect other birds with or without showing symptoms.
It is advisable (if it is mycoplasma) that the birds showing symptoms be put down and their bodies burned. It's that serious. This is why I recommend getting a blood test at the vet. If it's infectious bronchitis, that's one thing... Mycoplasma is a whole other beastie. At the very least, should it be mycoplasma and you decide NOT to cull, you will need to maintain a closed flock... Birds can come in, but no birds go out.
I don't mean to scare you... I just want you to be armed with all the information.
Let us know!