Scaly leg mite situation with mother hens, who have little chicks (pictures)

Finnish dude taking care of chickens and the first time in my life I heard about this thing 2 days ago after having 3 of the chickens (and a rooster who is no more) for a little under a year now and the one without the feather hat for 15 months.

I did not have any idea there was something wrong, since they all seemed perfectly normal in every other way (eating, drinking, other behavior, poo). Obviously now that I learned about this and observed them a bit I noticed a peck or two to their own feet and standing on only one feet every now and then.

Well here are my four hens, the three with the hats are a bit over 2 years old and the one without is 1.5 years old:

1 feet: http://i.imgur.com/pYKr5tT.jpg?1
chicken: i.imgur.com/pYKr5tT.jpg?1

2 feet : http://i.imgur.com/tarrzrm.jpg?1
chicken: http://i.imgur.com/KOsiUWL.jpg

3 feet: http://i.imgur.com/b4fdNKT.jpg
chicken: http://i.imgur.com/M7rcxrh.jpg

4 feet: http://i.imgur.com/j9PrYYI.jpg?1
chicken: http://i.imgur.com/j9PrYYI.jpg?1

Questions:

1. The 4 chickens have a total of 22 young ones (no symptoms), who are 2-3 months old. What would be the best easiest way to deal with this whole thing, since I'm on my own on this one. Any suggestions as solutions or any help at all to this problem (without killing every single one of them) are appreciated.

(Ivomec/Ivermectin and Stronghold have been mentioned the most often on the Finnish chicken forums. Stronghold apparently a bit extreme, but Ivomec has often been recommended by veterinarians. Will try to get some help from a vet obviously. Will see how that works out, not always the easiest thing to find here for small flocks of chickens)

2. When cleaning the hen house (6m/20ft x 5m/17ft x 2.3m/7.5ft) , getting rid of the old stuff (peat and straw mostly) from the concrete floor what would be the best option to put on there in this situation before I add a bit more when it starts to get too cold?

Will replace the roosts and other easily replaceable things, clean the windows, the levels under them and everywhere else they have been sitting every now and then a bit better, dust the wall and roof: http://i.imgur.com/KGrKUYY.jpg, and then vacuum and use some Virkon S on the tiny tiny gap or whatever you call it where the roof meets the wall.

3. Anything I should know about cleaning these places or any type of cleaning products that have worked well?

And ask away since I've likely missed some useful info, but I think at this point I'd just write useless stuff, and even fewer people want to read that.

Thanks