Like Jim said....they stop laying when they molt, so that is normal.
Almost all of my girls went through a massive molt and are just finishing up. The coop looked like they had a huge pillow fight every evening!
Why are you thinking mites? Are they skinny? Have you seen any mites? Are they acting sick at all?
Check their skin very close near the base of their feather, under their wings, near the vent. Mites can be hard to find and some types only get on the birds at night to feed. They live in the cracks in wood. At night after they are roosting, bring out a flashlight and check them very well. You may have to try several nights in a row before you find anything. IF they have mites....you will want to treat the coop and the birds, and then retreat again in 10 days (i think) to catch the newly hatched egges. I use poultry dust on my birds a few times a year as a preventitive and use the spray in their coop seasonally when i clean it out.
If the only reason you think there is a problem is because they have stopped laying, it's totally normal during a molt.
However, if they are skinny or unwell, I'd start checking for mites. A mite infestation can make the birds anemic and take them down quickly.
Andrea