Cinderella, if you have reason to believe that your brother is purposely keeping your parents in the dark about this, and if your brother is an older teen (17+), you should probably not talk to your parents about this behind his back.
On the other hand, if you feel that he would listen to them, then it might just be a good idea. But you might be burning a bridge here, if you’re on good terms with your brother and friend and they feel betrayed when you tell your parents “behind their backs”….
Just something to consider…