if you want the skill Auto Heal, you'd have to learn it. choose the Chemist job class and earn enough JP to get it. i think it's 400 JP or maybe more.
and buy lots of potions. if you don't want your characters to use potions, only buy hi-potions or better and don't carry any regular potions in stock. that way, you'll get 70 HP (or whatever) instead of the 30 HP from a normal potion. all depends on how tough the enemies you're fighting are.