there is Scaley Leg Mite that causes crust and raised scales.
There is also Bumblefoot that causes a puss plug in the soles of the feet..the infection is usually Staph..
both need treatment.
for Scaley Leg..some type of oil or vaseline, or Bag Balm on the legs to smother the mites and help condition the scales.
some people scrub the legs with a very soft brush before applying the Bag Balm..
then treat bird for mites..
Ivermec (ivermectin) is effective in treating leg mites and other critters.
can you post a pic of the legs and feet?
if it's Bumblefoot..they need Pen-G procaine injections..
available at farm/feed/livestock stores..usually found in the frig.
or some systemic antibiotic for treating staph.
the plug (raised area on the ball of foot)..needs attention..
for now..you can try making up a paste of sugar and betadine, and apply it to the feet, covering it with cotton ball and self stick bandage...to help draw the infection out.
but it might need to be lanced and the cheesy plug removed..everything should be sterile and area properly treated to kill and stop infection..washed with wound cleanser or diluted betadine..or iodine. antibiotic ointment applied and bandaged as above.
the hens should be confined to a safe area with food and water and soft clean bedding so they can rest the feet.
are the swellings hot?
it's possible they have both conditions.
how high are the roosts?
are there lots of stones or prickly things where they walk?
you can do a search here for Bumblefoot and Scaley Leg for more info. Lots of it.
for treating them for lice and mites initially..you might want to give them a bath with diluted Adams flea shampoo for dogs and cats..
antibiotics, insecticides, and Ivermectin is available at most farm/feed/livestock stores..or:
http://www.firststatevetsupply.com/store/
the ivermectin is listed as a wormer since it also gets rid of worms.
you'll have to thoroughly clean the coop, remove bedding, and treat..get rid of the old bedding.
what are using for bedding?
pine shavings is best...not straw or hay.