First, it sounds like you've never shot with two models before. And it sounds like one of the "models" may be very inexperienced. Here are my tips:
1. Print out some sample poses (with two models) that the 3 of you can use for ideas. You're not tied to the photos. But between your explanation, your ability to demonstrate a pose, and the photos, it gives you a range of ways of clarifying to the models "this is what I want."
2. I always tell models in tandem shoots that I want them to "connect." That doesn't mean they need to touch. But they should NOT look like two cute chicks standing next to each other, oblivious of the other's presence. Instead, I want posture or facial expression that conveys some form of interaction between the two.
3. Come up with multiple concepts for "frost." Temperature-cold. Relationship. White icicles (visual frost). Left out over night. B/c just having one concept with new models may be a bust--so try one and then move on. If all you have is one idea for how to go with "frost" and it doesn't work, than you're hosed.
4. Find out a bit more about the second model (height and dimensions) vs. the first. And then think generally about composition issues (if you want to put the taller model in back, create diagonal lines with poses, etc.).