If its a 2 set, you need to find a wing of some sort. The target is simply not going to completely commit her attention to you, as she has a duty to check her friend is ok. In this instance, the problem isn't the obstacle. Its the target's loyalty to the obstacle, and until you can find a way to be winged, its going to be difficult.

You can number close in a 2 set however. It involves talking to both of them, but there's no reason why you can't run your game and then towards the end turn to one of them and say 'Well I've gotta go see a dog about a man, but Helen, give me your number, I'll give you guys a call a bit later.'

Its possible to number close your target, but kiss closing her is going to be a whole lot harder.

A three set should be easier, but in the absence of a wing, you'll need to isolate her. There's not actually anything wrong with turning to her friends and saying, 'Guys, do you mind if I steal Helen for a little while?'

They're not exactly going to say no, and you've stated your intentions fairly well - saying 'I want to spend some time alone with your friend, please do not interrupt us'

But more than anything, find a wing. This shit gets a whole lot easier when you've got someone to work with.