That is my first thought, that they're wiping it off. But where is it coming from in the first place is the question. Did you get all of the chicks at the same place/same time? I'd separate the sebrights from the rest. Are they holding their tails up or down? If they're wobbly, you might try some PolyViSol baby vitamins (no iron) for them. Some things are vitamin related. Some things more complicated, and I'd be hesitant to get into that because I'm not all that qualified in some of the more serious things. I did have a little bantam roo die from apparent Mareks from what the necropsy said, but never showed the classic symptoms that a lot describe with it. I treated him for anything and everything. The only thing I can suggest is vitamins, unless you can see a specific respiratory issue. Puffy eyes is one sign, but that could also be maybe something in the bedding. All four showing symptoms though lead me to believe it could be something they picked up before you got them. I really don't have a good answer for you, I'm sorry. I hope someone more qualified can chime in on this when they're online. There are quite a few knowledgeable people here.