How to know if my hens have mites or lice .

I have been reading up about lice and mites and wanted input from this forum. I wanted to see how others look for lice or mites. I am just not sure if this it what it is but I notice two of my hens with some missing feathers. One is on her next under her waddle. The other is the back area and vent hole area. When I did a closer inspection I couldn't find anything . Tomorrow I am going to use a magnifying glass to see if I can see anything. I did notices one picking at her feathers. Another note I have 17 hens and I know its winter but I am only getting 4 some times 7 eggs a day. Friends of ours has the same and they are getting 14 eggs a day. Note they are using a lamp in their coop. I only use it when the temp is teens or lower. I have read also that mites & lice can cause low egg production.
In the readings I have been doing it talked about using ash from our fireplace and covering them with it and if I find nits to use NuStock on the area where I find them and spray their roost and coop area with Neem oil. I want to go naturally no chemicals. Any suggestion or is this a good way... I am doing deep beeding in their coop and it is probable a good 10" right now and I hate to empty that until spring. I do clean their poop area everyday and once a week add a bag of shavings on their floor and rake it in