Faction Friendly Fire in Arenas?

[RobagNetwork]

Hello, everyone. The last thing I have to do with my bending arenas is to allow friendly fire in the arena world only. This way faction members and allies can attack each other in the arena world, but friendly fire is disabled in the faction world. I've looked into using WarZone but this disables building, therefore disables bending since bending is attached to the build flag.
I don't know how to do this, so someone please help