I really don't think that he has to jam in the math and science. If he wants to, then fine. Yes, math through at least Calc BC and take all the AP sciences, but honestly, these courses will in no way guarantee his acceptance to those three schools.
And doesn't your school have other math courses? Linear Algebra? Diff Eq? Did he not take a language in middle school? Or does he want to start over with a different language in HS (most kids enter level 2 of the language in HS - AP is essentially level 5).
While I'm sure he will be a qualified applicant for those schools, most applicants are qualified. He may very well get in one of those schools, but he needs to "love his safeties" (i.e. apply to other schools where he knows he will get in).
Take a look at the stats of the kids who got rejected from those schools on College Confidential. Many of them had courses like your son plans to take. Then look at who got in. Sure, some won't make sense, but typically kids have won some high level academic competitions, have published research, have some very special talent (could be in the arts or sports), done an exceptional service project (not just Eagle Scout), etc. Of course, if you are first generation to college or URM, that helps, but I suspect that is not the case.
Help him find his passion and that will guide his ECs. 8th grade is a good time to plan this stuff since you really can't get really into an EC that you start in 11th grade.
My kids do not have those special ECs. Middle kid is taking 4 APs this year (11th) - AP Eng Language, AP Calc AB, AP Physics 1 and AP French. Next year is likely AP Spanish, AP Eng Lit, some AP science (Chem or another Physics - already took AP Bio), AP Euro, not sure on math. Plays two sports at HS, in 5th year of a travel sport, student rep to a Board of Trustees for an educational non-profit, perfect score on a national foreign language exam...she does not have anything special. Maybe could try the sports angle at a DIII like MIT, but otherwise, nothing special. Like someone else said, you need to play the game. Mine have not and it probably hurt my eldest in her acceptances.
