I would give the Tylan 50 orally or by injection at a dosage of 0.2 ml per pound of weight twice a day for 5 days. A 5 pound hen would get 1 ml, a large hen about 1.5 ml, and a large rooster more. Getting a rough weight with a kitchen scale or by holding the chicken while weighing it, then subtracting your weight.
The foamy eye could be mycoplasma (MG,) but the bad odor and thick nasal drainage sound more like coryza. It is unfortunate that the new birds have probably brought in a bad disease. You may want to cull the sickest bird, and get a necropsy to identify the disease. More than one disease can be present, if there are secondary infections. It can take weeks for chickens to get better from respiratory diseases, but the whole flock should be considered carriers. So sorry.
The foamy eye could be mycoplasma (MG,) but the bad odor and thick nasal drainage sound more like coryza. It is unfortunate that the new birds have probably brought in a bad disease. You may want to cull the sickest bird, and get a necropsy to identify the disease. More than one disease can be present, if there are secondary infections. It can take weeks for chickens to get better from respiratory diseases, but the whole flock should be considered carriers. So sorry.