If you are dying to know what's up, then instead of waiting for him or for your friend to bring it up, you should bring it up. Waiting may take a while. That's why if you want to ease some tension, you've got to make the move.
And what's so bad about your crush knowing that you like him? People act like if their crush knows that they like him or her, the world is going to end. I know that most of it is due to the fear of being turned down, but if he or anyone hasn't said anything about it yet, then there's nothing to freak out about. But I shall warn you to prepare yourself for the risk of getting rejected. Once your secret's out there, you have to be ready for the possible negative consequences it may brings. In this case, it's rejection. It may not seem so huge but it kind of is. To put it simply, rejections hurt and they suck. But if you are more prepared for it, you wouldn't be as shocked and the pain would be less so. Be aware that I am not saying that he will reject you, I'm just saying that you need to keep your guard up.
And what exactly do you want to tell your friend who is the sister of your crush? Do you want the whole story, confirmation, or what? Keep whatever it is you want to discuss with her in mind when you go and bring up the subject with her. Therefore, it reduces any awkward pauses or silences.
I hope this helps a little. Good luck!