Now that you say that, I remember! I would just caution folks to be sure to calculate dosage based on your chickens' weight (the bottle talks about calves, but yes we use it off-label for chickens).
It works better that way. Been a while since I looked it up, but there are different dosages of amprolium you give your chicks depending on what you're trying to accomplish. The level in feed is the lowest, just enough to kill some amount of cocci in their system and keep the level low enough...
I looked at the pics you loaded of the feed bag analysis tag and date code. Nov 2022 is recent, 18% protein is good. The methionine is a little low, so if they were not sick and taking Corid, I'd say give them some vitamins that have B vitamins in them. But for now, I'd leave it until they're...
There are other options out there, but this stuff has worked great for me, and a lot of folks on here use this for our backyard flocks.
https://www.purinamills.com/chicken-feed/products/detail/purina-flock-raiser-crumbles
That permethrin poultry dust is good stuff for mites. Long as you're sure they were mites, that should do the trick. Might want to put the lamp a might closer, say 90F, since they're sickly, as long as they can still get away to cool off if they want to, if they're acting cold. If not acting...
Have you done a fecal float for these guys? A veterinarian can do it for a minimal fee if you take them a fresh sample of poo. If they'd been running around outside before you got them, they could have intestinal parasites (worms, who knows). The treatment varies depending on what they've got...