Yeah, lots of practice and luck...
Well, okay, maybe not just that. If you use the spells Divine Might (the one that increases damage) and Weaken Enemies (that reduces their resistance against that damage), then that helps a lot. I was defeating them one at a time with Unarmed in the end.
Trying to separate them any way you can is useful.
I think I opened a sarcophagus in Stealth mode, sneaked away and then returned slowly after a short while so one of them would see me and follow. One at a time is far more managable than 2 at a time.