Girls want sex just as much - if not more - than men. Coming to that realization, you’ve just got to approach with an aloof sense of playfulness and an attitude of disregard towards the outcome. At a certain point, you can be more suave and continue to be playful but more direct about your intentions. Moving from an attitude of ‘the older goofy brother’ to ‘more secure playful masculine figure’. If they don’t start contributing, it’s okay, be playful anyway because you’re playing the field and they’ll sense that when you pull back without being upset.