So that’s all great- but what is the goal, his underlying thinking? Is this a competitive thing? does he think it will give him an advantage in grad school apps? (almost certainly not). Are these three subjects the only things he wants to do in college? Whatelse is he going to do in college?
More practically, how is going to do summer REUs/equivalent (which will matter way more for grad school) if he is doing summer school for his humanities? Is he going to have time to take grad level classes in his ‘core’ major (again, will matter way more for grad school)?
Tbh, though, parent to parent, I would wait and see what the advisor says. IME they often will hear things from a teacher or advisor that they won’t from a parent!