The classes are attended just by preppies by they are taught by an academy professor and follows the same curriculum that cadets have. It's Calc 141, I believe. And yes, those C/C picked for one or both classes can get up to 6 credits. For my daughter, it's a great thing because she wants to study astro and that's one of the hardest majors.
As for your son, I have no idea. I know people keep throwing numbers around, but the truth is that no one really knows what the academy needs at any given time. With my daughter, it was a shock, because with all the numbers I kept seeing around this forum, I didn't think she would get the chance, but instead she ended up getting a LOA for the Prep back in November. I would think with someone like your son and with his grades, he's more likely to go straight to the Academy, especially since I remember reading that he already has nominations for all 3.
My one unsolicited advice is make sure that he goes back to visit. My daughter was so sure about the Navy. For two years, I heard nothing but Annapolis, but once she visited USAFA, she changed her mind overnight and switched her nomination preferences for USAFA.