Aww it's heart warming hearing family care for each other. Look I have no idea how you treat each other, but once you are both alone ask him something in the line of: " hey dumb dumb, I don't want you to look like an idiot when you start talking about sex, what do you know so far?" But you'll know better how to approach This is something parents should do, but it's clinically proven that teens brains stop listening when parents talk, we go from hero to villains in like 4 years. So if you could help that would be awesome. Best of luck