With my first character, as a Warlock I killed them without any problem. Later I made my Ranger and they killed me from one single hit, I did not even save my game! After do it all again and save, they managed to kill my second character (cleric). At the third try I was able to pass them but almost died. Later on, with another character i had no issues, like mir first character. I think this encouter is a little bit unbalanced. If you pass the checks you kill them easy. But if you don't pass it... they slaughter you.