He might be a little too old for this at 9 years old. I am not sure. Every kid has a different maturity level. I bought this series for my son.
http://store.crickett.com/my-first-rifle-story-book/
He is going to be old enough to hit the range with me on the 4th of July, his birthday. I read these to him at bedtime (I doubt THAT will apply with your brother). He can almost quote it, word for word, as I read it to him. After the recent tragedy, when the little boy shot his father in the abdomen, we discussed it as we do every publicized weapon tragedy (be it firearms, bow, knife, etc.). I asked him what he thought went wrong and my boy told me that he broke the number one rule of gun safety; Never point a weapon at anyone! Repetition, especially for the younger kids, is imperative. Even though these books might be a bit juvenile for him, they are FULL of invaluable information.
You said, "I've thought about doing stance practice and dry fire but I'm not quite sure." I would say that this is very important. You want to make sure early-on that he knows not to sweep the firing line, keep his itchy finger OFF of the trigger until ready to fire, etc.
Do well!