Forget what the manual says about the Mortuary. It's not really a dangerous place, and you don't have to fight your way out. The Dustmen are caretakers of the dead, and killing one of them would be like killing a mortician in real life. If they see you walking around, they can only assume you must be an intruder. All you have to do is avoid them and you can leave the Mortuary peacefully. As weird as it might seem after playing other games, the zombies in Torment are not bloodthirsty monsters; they're just corpses who are programmed like robots by the Dustmen. They aren't dangerous at all unless you attack them. You have to kill the first zombie you meet to get a key, but after that, you don't need to kill anybody at all.
Instead of killing the giant Skeletal Warriors (which is practically impossible at your level), the best way to handle them is to find a book that one of the zombies is carrying and use the instructions in the book to disarm the Skeleton Warriors. You'll get 800 experience points apiece for that. You'd get far less experience than that for killing them.
This game is less about combat than it is about finding clues and recovering memories from the Nameless One's past lives. If you make all of the zombies and Dustmen hostile, you won't be able to talk to any of them, and you'll miss a lot of important clues and also a lot of experience. I once added up all of the experience you get for killing everything in the Mortuary, and it was only about 800 experience points or something like that. But if you TALK to all of the zombies and examine items and talk to a couple of the special characters in there, you'll go up in level a couple of times. So just remember that you get more experience for TALKING to people than you get for killing them. That's not what you would expect, is it?
Thugs in the Hive are easy to avoid. They won't chase you unless you walk too close to them. If you do get into a fight, don't underestimate Morte. He has very high damage resistance, so he can kill a lot of lesser monsters before they can kill him. And don't forget that you can enable "running" in the game. I used it all the time.
I've given other people a lot of hints about how to play if you want to check out my other messages with the search function. But my general advice is, don't try to play this game like you would play Baldur's Gate.
Good luck!