Currently group dueling doesn't work. I'm not sure exactly how it is supposed to work, so I can only describe what I tested.

Group 1: three people, A, B, and C
Group 2: one person, Z (note it was actually a group with one person in it)

Z challenges A (the leader of group 1)
A accepts

Z and C are on the same team and normally can't damage eachother.
After the duel starts C can now damage Z, but Z can not damage C.

If B or C damage Z the duel is ended as if it were a 1on1 between Z and A.

this bug is still around.