A little worried

I'm a little worried about soe of my high school friends back home. I'm not one to judge. Everyone is entitled to do whatever they want, no mater how self-destructive it may be. But a couple of my close girlfriends still in high school are taking those first few steps down paths that may not lead to happiness or success, which is what I want for them more than anything.
My one friend, who has always been very intelligent, some-what free-spirited, and a social butterfly doesn't seem to be making the best choices lately. She smokes pot constantly, and never goes to school. Look, I realize this time of year sucks. It's senior year, everyone is and has changed from when you first met them. Teachers are giving you meaningless busy work and you really begin to outgrow all of the bull shit rues and regulations around you. Senior year sucks. I get it. I know you're gonna have to take your exams anyway (since you have well over 10 absenses for the quarter) but you do realize that if you miss too much school, you kind of won't graduate? This girl is so smart. Could probablly get into any college she wants, but I'm afraid that with the drinking and smoking out nearly every night, she's going to become a total burn out; someone who can't function normally in society. I don't want to see her in a year or two and be devastated when I remember how driven and vivacious she used to be. I of course can't come to her with this. She's a hell of an arguer and more importantly, it's her life. I can't tell her what to do.
My other girlfriend is dealing with other issues. I'm worried about her emotions and self esteem and just her overall feeling of self worth. She's been hooking up with (not dating because she said she didn't want a relationship) this 16-year-old boy (she's 18) who she just found out hooked up with another girl. Despite their "open-relationship", this of course crushed her, or it least she said it did 3 days ago. I call her today, however and she's back with him and tells me that they're just using eachother for music and sex. I don't know why she's so insistant on having a dead and emotionless relationship. It kind of scares me.
On top of that, after to applying to and auditioning at numerous prestigious music schools and universities, just like I did a year ago, she finds out that she's been rejected by her top choices. I'm pissed because her mom, the crazy batch that she is, insisted on making her apply to all of these nearly ivy-league schools with literally no safety schools. So, my friend, being an incredible musician but an average student, was rejected from several of the schools she worked her ass off auditioning for. Her mom just has to find a way to bring her down and make her feel small and that fucking kills me. I want her to know that she's worth so much more than a stupid horny 16 year-old boy and 2 college acceptances.
These girls are so close to me and I'd hate to have them lose themselves.

I don't know what to do.