If there is nothing physically or mentally wrong with your child, then it is time to for punishment that does what it is supposed to do- make him mind you. It will take some work on your part. Each time he soils himself, make him clean the mess up- wash the clothes out in a bucket outside. For #2, make him rinse them in the toilet first. Then, send him to his room for several hours, bringing him lunch or dinner to his room if it runs over eating time. (Also, no TV, video games, computer, radio, etc in his room) He can look at books and play with simple toys but he must stay in his room.
Make sure you explain to him that he cannot go to school, friends houses, etc unless he is using the toilet like the rest of the kids. Maybe you could get your 7-yr-old involved in helping with this.