Just killed him first time on hard with main (cipher), Eder, Aloth and Durance all lv 4.
I used paralyse and mind blades with my cipher, only shooting once with a pistol to restore focus (onto a paralysed enemy) . Eder tanked. Aloth used Fan of flames 3 times, expanded region on Eder. Durance used Blessing and then did some healing.
It was over quite quickly.