For Mites, check your coop and the birds at night, look around their vents, under the wings, etc. Wipe the roosting bars with a paper towel and see there's any bugs or smears.
It would be a good idea to spray down the coop, roosting bars, nesting boxes with a Permethrin based poultry spray. For the birds, I prefer to use Permethrin based poultry dust. Put the dust in a sock and use it like a powder puff to dust the birds, working the powder all the way down through the feathers to the skin.
Do clean out bedding before treating housing, either throw it away or burn it, don't compost it. Repeat treatment of the coop in 5-7days intervals.
Rats can be hard to get rid of. Put feed and water up at night. Start trapping. I put traps under a dish tub or some protected area where the chickens can't get in the trap. You'll trap some, but not all. Depending on how you feel about it, bait stations can also be used just put them where other animals and the chickens can't get into them.
If you are feeling them on the skin, it would be a good idea to change and launder clothes after tending the chickens.
https://www.backyardchickens.com/threads/mite-infestation-starting-new-post.1630760/post-27847239
