I don't think it would be Marek's if they have closed puffy eyes. It sounds like something respiratory that is spreading quickly, and I assume all your Rocks run together, as most birds that look similar tend to do. I would suspect ILT (infectious Laryngeotracheitis) possibly, which is extremely contagious, and kills quickly. There is a vaccine for it, an eyedrop, which you can administer to sick and well birds. Yes, you can do your own necropsy, for ILT you'd look for a (basically) shredded throat on the inside. It is a horrible disease. But there's no guarantee that's what it is, and for the best results you should use someone who does necropsies professionally. If you're in the States, call your veterinarian or your State agriculture department. Depending on where you are, it's not expensive. Or, search on BYC for a fellow member in your area who has experience doing them. In the meantime, if I were you I'd try treating your sick bird with injectable Tylan, which should be available to you at the feed stores if you're in the US. And you can wash her swollen eyes with human ( plain saline) eyewash, and follow that up with triple antibiotic ointment (with NO pain killer in it) applied carefully on the closed eyes, or around the eye, with a clean finger tip or q tip. For the rest of them, I'd at the very least put them all on vitamins/ electrolytes right now, as well as sanitizing and disinfecting everything else possible. Do remember that you are on a ticking time bomb right now, you have to keep a close eye on all of them and treat as much as you can as quickly as possible. If your sick bird dies, you have to have a necropsy done within twenty four hours, and refrigerate the body if possible. Or, if it looks like she will die and you can't save her, a professional doing a necropsy can and will humanely euthanize her for you, prior to doing the necropsy. Good luck, I'm sorry you are having to go through this, it's a nightmare. Please keep us posted.
Also, I read recently that' there's an antibiotic powder you can get for birds, called ALL in One. I personally wouldn't use it, because imo it is so broad that it would build up resistance to a lot of antibiotics if used over time, BUT if you have absolutely nothing else you can try, that might be worth a try. You can get it on line, so i've read. It has several antibiotics in it.