They whoop my ass hard.
I don't understand how I'm supposed to beat them; I can hardly hit them, while they take away my health (100) so fast I die in a few seconds, fully healing up with roots/potions extends my life with about 2 seconds.
I've expored this whole level, killed everything I could find, there are now some locked doors and chests, and maybe some secret areas I didnt find, although I doubt they are essential to beating these guys.
I'm using a sword (lvl 2) from one of the secret areas, I think it's 1 step up from the standard sharga sword, and a shield (lvl 1). I got the pants armor, chest and helmet.
My strength is 3, agility 2 and health 3.

You are not supposed to kill them. You have to sneak by them or be quick.

Well, I know I have to kill them, because 1 dropped the steel key and the other drops an important orb item. Besides there's no point in sneaking by them, because you can just enter the room from the other side.
I killed them a few hours after I posted this topic. However I resorted to an extremely cheap way; I threw an oil bomb while they were non aggro, then ran the fuck out, stood in front of the open door so they couldn't attack me and threw my other 3 oil bombs at them. Then I threw rocks and 1 of them died (after missing a lot). I still avoided close combat for the other one by throwing daggers, it died after 2 or 3 of them. 2 or 3 times I ran across the room, just to reset their position, thinking it would be easier to aim (though I'm not sure about this at all). So basically throw everything I have at them, while they can't hit me. Really classy tactic..., but I don't see any other way how I could kill them, as close range is out of the question.
Really I'm not sure what the developers were thinking. I mean talk about a steep difficulty curve; first you're walking over ants, then you kill sharga's that are easily disposed of, next you're fighting 2 really strong ones that hit like a truck and destroy you in a few seconds. Makes me feel like the angry videogame nerd thinking about this.

I'm still curious how others have defeated them, since I don't get the impression this fight was an issue for others (lack of mention/posts about this), while to me it seems very unbalanced.

You can steal it form them when they are sleeping or something. I'm sure because I remember that I didn't kill them.

Heh, I used exactly the same tactic to kill them. Definitely one of the most difficult fights in the whole game. (As I think of it, perhaps the second level was the hardest in the game, as well...)

That fight is very hard but you can kill them without "cheating" if you are careful; the trick is to move around a lot. This makes it much harder for them to hit you. You can back away from them and throw things, then when they approach you can quickly turn twice and start backing away again. This makes it hard for them to hit you. You can even fight them in melee with this technique, by quickly striking when they come in range and then turning and retreating again.

Definitely one of the hardest fights. The game actually gets easier later on when you have better equipment and some party members.

High arrows and oil bombs are quite destructive. It IS possible to defeat them in hand-to-hand fight, though. You can, for example, train your weapon of choice in armory...

One of most difficult fights in Stonekeep - I totally agree. And that is the fun. :>