Just talk to the guys in the group. You don't even need to talk to the girls in the beginning. Directly approaching girls in a big mixed group might trigger some alarms in the friends (for example if the BF is among them). By approaching the guys first you can screen for these kinds of things and then act accordingly. A lot of times if the guy you're talking to is a bro, he will introduce you to the single girls or you can ask him to do so.

tl;dr By approaching guys in a mixed group you can screen for logistics of you target much easier and potentially get introduced to her which effectively turns you cold approach in to a warm approach.