Is this scally legs, if so how should I treat it and what are the chances that my other girls have it to?
Once a week bring them inside, and soak the legs in warm soapy water. Take an old toothbrush and gently brush the scales to loosen them. Rinse and dry the legs well. Then apply either castor oil, vaseline, vegetable oil, or other favorite oil to legs and rub it in so that it gets slightly under the scales. Don't use kerosene or motor oil, please (this has actually been advised in the past.) It may take several weeks to see new scales starting to grow in. Your other birds may well have it, and you may want to treat your coop, nest boxes, and roosts. Permectrin II spray works well for a coop clean-out.
X2, though linseed oil thinned with a little kerosene works great as an underside roost paint, I wouldn't recommend it as dip for the legs. Don't smoke while you do it, lol. Treating the roosts is important for controlling Knemidocoptes mites. Treat them every 4 weeks with a kickass emulsified concentrate like Ravap EC, Tempo WP, Rabon 50 WP, or Atroban 11% EC. Be sure to apply under, on the sides, and tops of roosts. let it dry and allow birds back in the coop. ScienceChicken, applying oil like Eggcessive mentioned may need to be done 2-3 times a week until it is under control. Nustock mange medicine works very well due the pine oil and sulfur. Wear nitrile disposable gloves and massage it into and under scales.