8-10 inches? Yikes.

Start this simple drill: Put your feet together and point your toes 45 degrees open to the target.

Once you have about 10-15 shots that hit the ball, spread the feet apart a little, but keeping the toes where they are. Hit another 10-15. Next, point the toes back to the ball. And see that happens. I bet you are now not swaying back so much anymore and keeping really good balance.

If not, and you were never able to hit the ball at all? Your step son might be onto something...