There are friends who you can work with, and there are friends you can't. Some of my friends I would trust with anything, and some I get uncomfortable when I leave them alone in my living room. It sounds like your friends are fun, but I wouldn't loan them my car.
First, I'd talk with them seriously in a setting set up for just that. NOT in passing or at a gig. "Guys I'd like to meet for a few minutes for a meeting, when can we meet?" Sometimes people don't realize when we are being serious.
Tell them you are worrying and that you need some groundrules to put your mind at ease. DON"T judge their behavior but DO list what kind of behavior that you need to work. This puts the ball in their court. Either they can respect your needs and change or they can chose not to, in which case you have reason to become annoyed and take action.
If your friends are not respecting you, then that's a problem. If they are not respecting you and know it, then they are not your friends.