I haven't use the editor for any of the party but I noticed as soon as I upgraded the Reaver specialization on Bull or a Warrior character, my companions start dying around me whenever there is a Warrior in my party. I'm really confused.....
If you don't use god mode and you have friendly fire on, some 2h weapons by default do AoE damage, including to your party. A lot of 2h abilities also are AoE including whirlwind and shattering earth.