Similarly (and this is one of the issues that initially sparked this idea), you can't have cross-family interactions that both address the same variable, since a family can only check variables that it has.
You have a Yin family and a Yang family. When a Yin they collide, you want them to reduce each other's Power variable by the other's value, and destroy if it hits 0. (So if a 20-power Yang and a 10-power Yin collide, the result should be a 10-power Yang and no Yin). Under the current system, there's no way that both families can have the same variable in common.