In my experience, with any team for PvP, the only character that has to be soaking up a LARGE amount of damage, is the main toon. If you want to have a toon that breaks the rules of damage dealing in order to soak up as much damage as possible, regardless of losing >50% of his damaging potential, the main toon is the only one.

Beyond that, the 3-4 slaves should be geared towards as much survivability without gimping their damage much at all. The only time that they will really be getting focused is when your opposing team is smart enough to know that they are squishier; but 95% of the time, the main toon is the only one that takes any focused damage.