I need help with a situation I have found myself in. My girlfriend's younger sister and my younger brother are good friends (not together, just friends). Recently I heard through "anonymous sources" that my girlfriends younger sister wants to try smoking pot. Now, as me and my girlfriend smoke, I'm not against marijuana. But she is a little young to be trying it I think...and my brother says he won't remain friends with her if she does. Also, the guy she wants to try it with is someone who quite frankly just gives me the creeps. So what I'm asking advice on is simply what do I do? Should I tell my girlfriend? Should I intervene in any way? Any advice would be greatly appreciated. Thank you.