The graybeards, or are they all invincible? Just a quick question

Why don't you try?

I have but they always kill me before the bar depletes haha

I tried killing the Arch Mage. Took his health all the way down but he just sat there for a bit on his knees and regenned all his health back. He did this 3 times in a row and after that I presumed he was just invincible

Annoying because I wanted to be a evil thief type who just kills everyone and takes their stuff

Lower the difficulty in order to test it, then use FUS-FUS-FUS until you lower the health bar and use FUS-RO-DAH......then beat them up with swords....and you might have to beat the main quest first.....