If healthy and just stunted, water and fertilizer will likely return them to normal growth. Certain apples on very dwarfing rootstocks can become runted out to the point they are difficult to rejuvenate. Usually that only happens if they are allowed to overset fruit.

Depending on how they look some pruning might be in order. But if they haven't grown much that might not be necessary. I'm thinking some heading might be in order if the top growth is small and twiggy. But only head if you want them to grow taller. If the height is OK they might be ready to fruit.