Well, I have to ask this: You say they won't listen to you but are you listening to them? I don't mean convert or agree but just listen. They start wanting to open and discover new things but it doesn't mean they will leave their primary faith. They're just looking and curious. I think if you refuse to even hear what they are saying or yakking about, it might cause problems. Maybe let them talk until they realize certain beliefs really don't go along with their beliefs and the curiosity is gone. My sister really changed her Christian beliefs after going off to college and some class she took that made her seriously doubt her faith. But, it all fell away...but I think it would have fallen away sooner if my Dad had just listened to her and not told her she was going to hell. I know I sound strong but I think this is part of growing up and maybe, just maybe, they just want to explore with you listening. I sure wouldn't worry about them.