I'm running a Dresden Files campaign and I'm starting to introduce White Court Vampires as enemies to my PCs.  I'm having some difficulty figuring out how their powers work in combat:

The Emotion Touch power says "If you can touch someone, you can make him feel something." how do you determine if you can touch someone?  Is there an athletics check?

The Feeding Touch power says "When a victim is in the throes of an eligible emotion, you may draw some of his life force out of him to sustain you."  How does this work?  Does this inflict more stress than Emotion Touch alone?