It depends on how deep they are, I suffered from them greatly in Highschool and college being on the diving team, I waited till I was done being in the water and public pools on a daily basis till removing them as they would just come back over and over again, If they are deep freezing them off is the best route, I don't think it would be more expensive by much if you have a couple done at once, you are just paying for the doctors slot basically. Duct tape works well for small ones, but you have to scrap off the top layer of skin first, and then scrap off the wart after you are done, Google duct tape removal of plantars warts. Warts spread through water the best so public pools the bath tub etc. He can reduce the chance of them spreading by wearing shoes when walking in water. I feel for him as they are bad. Oh and if he has any on his heals I never ever had luck with getting those off with just take only freezing.