I'm a Health Professions Council registered graduate Podiatrist.
I would be concerned about the amount of cryo he is having, if you over do it the vp (verruca pedis) goes but you can cause scarring to plantar skin (skin on the bottom of the foot) with cryo and when you get scar tissue on a weightbearing area you get corns.
These build up quickly in RhA patients anyway due to thin skin from previous steroid treatment and loss of fatty padding due to toe clawing (the toes move backwards and pull this fatty tissue on the bottom of the foot with it to expose the tender head of the bones).
In the case of scar tissue they can form in 3 weeks, as opposed to 8-10 weeks in non RhA patients. And there is no cure, only management to control the pain. Imagine having stone strapped to the bottom of your foot, that's what a corn feels like.
If a chiropodist/podiatrist did not originally diagnose these lesions as vp I would go to the NHS one to get a diagnosis. I cannot tell you how many referrals we recieve for patients with vp only to find it is corn. I know you would imagine a GP knows the difference but you would be wrong. They often dont. They dont recieve a great deal of training to do with feet.
If it is a vp, and the RhA is active it will be very difficult to get rid of, their immune system is so busy attacking it's own synovial linings it really hasnt got the time to worry about a virus in the skin.
If it is a vp do not self treat with acids, especially with Salycillic acid, as it is not self limiting eg some acids only work for 24 hrs but sal acid just keeps burning, even down to bone. And if he gets an ulcer due to a burn it will be very hard to heal. He will be down at a chiropody clinic every week having it dressed and not able to bathe it at all until it heals which can take 6 months or longer.
Whilst you are waiting for a NHS podiatry appointment ask your gp for Doublebase gel in a 500g pack. Apply it morning and night, you will not need to rub it in you just smooth it over the skin and put socks on and it will still soak in. It does not mark bedding. This will soften the skin and put it in better condition to recieve any treatments.
For shoes he should try trainers. They get a bad press but they are fantastic for cushioning the feet. If they make his feet sweat then spray them with normal anti perspirent before putting socks on.
Shoes with normal soles are just not as good at dealing with the pressures on the foot generated from walking. I wear mine every day for work and never get aching feet. They dont need to be expensive, he's not an olympic runner so he doesnt need any fancy technology just a well cushioned roomy shoe. As long as it fits with room to wiggle the toes and has a lace or velcro fastening, NO SLIP ON styles.
hth.