Well if you can control a 21 year old ADULT then more power to you, and maybe let me know how it is done. haha My friends DD is going to the DRC in a few weeks. I said the same thing, OMG how can you let her go, you need to tell her no. Well, yes, in theory that sounds great, but when they are an adult then you don't have much say. It is hard when they are in the age where you still feel like you should be able to control them, but yet you really can not. I am super proud of DD for doing her trip. I never ever would have done that at her age. Truthfully, I would never do it by myself now! I am definitely a cautious chicken and have to admit I am a little sad for myself that I would never get to experience the things she is doing. In theory I want my kids to explore the great big world, but in practice I really would prefer to say nope, stay at home where I can protect you. DD18 got picked to go to Ecuador in the fall for a one week trip so joy for that.
I did stop DD's travel soccer though for similar reasons as yours. It just got to be too much travel and time away from all of us together. We are Catholic, so we were somewhat adaptable when they had games on Sundays, fine we will do church on Saturday night. One year I even changed churches because the games were interfering with Sunday School times so I switched to a church with before Church classes instead of after. I tried to adapt a lot then finally said enough. It took her awhile to get over that I made her quit, maybe she still hasn't. lol
Since your trips are pretty predictable then you do have much better chances of not having schedules mess them up. Just say not to sports and band. lol Wait, weren't you in band? High school and middle school band was terrible with band camp in the summer. I was pretty happy that mine were quitters after 9th grade.