You are welcome @chris17mom. Drumline features the percussion section, as you might expect from the title. The bands are “show band” style, which probably isn’t very common where you are (it wasn’t when I was in AZ and CA). But here in Ohio one major university features this style (Ohio U) and many high schools (including our kids’ HS). So it may be a bit different if you aren’t used to that. But it can be fun.
On the theatre side (since we are on the MT site!), a smaller school (like NAU) might have more opportunities for doing both theatre and music. But it will be tough from a time perspective as music groups will typically rehearse 5-6 hours per week, sometimes less for small groups, but definitely a lot more for marching band (we had 9-10 hours of rehearsal not including performance time). And theatre does even more if you are in a show.
But if he is interested in theatre, same concept that I mentioned earlier applies - get in as many shows as you can. Could be school, community youth theatre, etc. You will also want to research the technical degrees (BFA for theatre and BM for music) and compare with BA degrees. If you want music education that will be a BM degree. Those, like the BFA, typically require an audition prior to acceptance. There are plenty of BFA v. BA threads on this site to give you some info. I haven’t been to the music majors site in a while, but I expect there is stuff over there as well.