if you have to ask this question, you shouldn't
unless you know them all well or are extremely charismatic, trying to approach a set isn't the best move, mystery and other PUAs can do it because they're pros, they also have like 50% close rates, it's not a great idea unless all the variables are in your favor.
however if you want to you still can, but just remember you're playing this game on very hard mode right now
if you must, get a wingman to try and distract the other girl while be more appealing than the guy(her male best friend) so she pays more attention to you