If "Raikou & Suicune LEGEND" attacks "Suicune & Entei LEGEND", how is weakness calculated?
Since "Suicune & Entei LEGEND" is weak to both of "Raikou & Suicune LEGEND's" types (Electric and Water), you would multiply the damage x4.
Source: Unleashed FAQ (2010-05-13), PUI Rules Team (2010-05-13)