Have you considered that they could be happy with how they are now? Not to be shallow, but my best friend is good friends with a lot of "not so popular kids" and I still hang out with him even though I am known as one of the "jocks" or more popular kids. My advice to you is to just hang out with them, but become friends with everyone and you can always hang out with your "popular" friends. They only thing you have to be careful of is don't become fake, like at prom yesterday I was sitting with the more popular group and my best friend walked in with his friends and one of the kids I was with said something rude about my friend so I let him know "hey man ---- is pretty cool dude but dont talk sh*t cause thats my boy." Basically, don't start talking trash about one group behind their back to try and sounds cooler. That's my two cents.