If each type had a super power, what would it be?
Ideally the super power should have an inherent weakness (as super powers generally do), and dual pairs' powers cover each other's weaknesses. One's conflictor could also be one's "natural enemy" (like fire and water). If someone's feeling really ambitious, activity partners could make each other's powers stronger, and relations of supervision/benefit could also be worked in.
This is meant to be something of a brain storming session though, so don't get too caught up in making the intertype relations fit. (: