Oh, I'm so sorry they have ended up having parasites. I believe coccidiosis is pretty common in chickens who have been moved from one place to another and get introduced to new microbes to which they have no immunity. From what I have heard, Corid is a good solution for that problem in particular -- it is easy to administer and seems to work well. I have read often than it clears up quickly and the chickens perk up soon after starting the Corid.
De-worming is another issue and you might want to get some more opinions and read around about; people have a lot of different opinions about handling that.
It is also true that all chickens are carrying some mite load; the question is whether it is at a level unhealthy for them. The other question is what kind of mites: some live in the coop and emerge at night to bite the chickens while others stay on the birds. So a couple of things you might want to do to determine the mite situation are: 1. check the coop interior at night with a flashlight and see if you see any on the roosting bars, etc; 2. check the birds themselves at night -- usually if any mites are going to be visible, they will be around the vent area (you might need someone to hold a flashlight while you pick them up, or else use one of those lights you can strap to your forehead). If you decide you want to treat and are OK with pesticides, I think people use something called permethrin for mites. (There are several threads on mite treatment here, from chemical to natural/essential oil; those threads are very helpful for determining if you have an actual problem.) I went the essential oil route when I had mites, but I don't want to bore you with that whole long protocol unless you are interested.
Good luck! One thing that has been suggested to me to increase chickens' resistance to coccidiosis and worms is to give them a probiotic every once in a while to strengthen their internal flora and immune systems. But that is just for maintenance -- it won't treat an actual problem.
I'm sure others will have useful thoughts and opinions, too.