Would he be interested in the Music Composition major in UCSB’s College of Creative Studies, or is that too “classical” for him? (CCS students can do double-majors outside of CCS.)
Has he considered Occidental? Their Music BA could be a good fit, with multiple focus areas including composition. Whitman seems like a great option too.
Denison could be worth a look: Bluegrass Goes to College | Article | Denison University
U of Utah, with WUE reciprocity, would cost less than a UC. They have a strong Honors College, and drumline… a very strong music department with a BA that’s designed to allow double-majoring, and solid programs in his other areas of interest.
Boulder does have a lively music scene - could be a very fun place to do what he wants to do. Much pricier than Utah, though, and the two schools have more in common than many people’s first impressions would suggest.
How about Weber Honors at SDSU? There’s drumline here too, both BA and BM options in the music department, and solid programs for all of his interests.
URochester is wonderful for musicians with other academic interests, and particularly good for crossover areas like music cognition. (The conservatory musicians are on the separate Eastman campus, so it’s more of a level playing field for the BA and non-major musicians on the river campus, which has its own facilities and ensembles.) They meet need and give merit as well.
Would the no-merit privates be affordable after the older sib finishes college?