What can I do if my dad has ingrown corns and callus on his feet. Help?

Pressure. Callouses develop when there is too much pressure and friction in the area of the foot. First par it down with a file. Then use spray deodorant (the armpit kind) to decrease sweat, this decreases friction. If that doesn't help, try otc inserts from a drug store to help off-load callus area. If fail, he may have a foot deformity or other pathology. Lastly, see a podiatrist. Hope that helps!
Corns and callouses. Can't be "ingorwn." they may feel painful and deep, but they don't grow "in." they are usually a symptom of a structural problem of the bones which cause rubbing on the floor or a shoe. The skin thickens as a protective response to the pressure. Do dad a favor and bring his feet to a podiatrist. You'll both feel much better afterwards!