Hello. Thank you for writing.
Most mouth sores don’t need treatment. However, if you get mouth sores often or they’re extremely painful, a number of treatments can decrease pain and healing time. These include:
-using a rinse of salt water and baking soda
-placing milk of magnesia on the mouth ulcer
-using over-the-counter benzocaine (topical -anesthetic) products like Orajel or Anbesol
-using a mouth rinse that contains a steroid to reduce pain and swelling
It sounds as though this person you are caring for is very ill. We cannot know what these sores are or what is causing them. You should contact his doctor if he is as ill as you say.