A cream, rather than lotion, will help to penetrate and soften the skin. A generic one is fine. If there is accompanying heavy skin build-up, gently use a pumice stone or pumice cream once a week to exfoliate. I soak and scrape them all of the time. These areas often hurt.
Salcylic acid is ineffective.
Change cotton socks twice a day to decrease wetness. Some plantar calluses are caused by excessive pressure from a dropped metatarsal. An X-ray must be used to diagnose this. Reduce moisture to the feet by wearing poly-blend type socks which help wick moisture away from the feet. Use a good foot powder and have several changes of shoes available.