I would do whatever is recommended by dawg53 (lots of experience and has helped me before too)! Some chickens just aren't as genetically healthy as others, and maybe that caused their egg-problems too. Also, just in case, you might check for any bugs on them in the vent area. Sometimes mites/lice can make them look really lethargic and drain their energy. I just treated 4 birds this morning with a drop of neem oil under the tail and I expect them to perk right back up tomorrow once the bugs are dead. Your situation sounds more serious than just bugs though. I'll be thinking of you and hope something works out for you.
I don't think I would use Tylan since it doesn't sound respiratory. If you don't find the corid, another antibiotic you can use for cocci is Sulmet, which they often have at the feed store. Be careful not to overdose with it though, since it can be toxic. It's 1/2 tbsp for a quart of water I think (check label to be sure). You can dip their beak down into the treated water to make them drink some every hour or so, assuming they show no interest in drinking on their own. Just be careful not to hold the beak in the water longer than a second at a time since they might inhale the water and drown. They need to lift their head up to get the water to go down between sips of water (I'm sure you already know that, but, just trying to help with anything I can think of).
