The tutorial/learning curve is the only hard part about this game. It is frustrating in the beginning and you die often. Here is my tip to get past it. save alot, and RUN if it seems impossible. At first, you need to click on top right icon to select and play as the death knight. Now near top right is option to "Select all" You can now fight and control both people at once. You can right click items to send to opposite character if it suits them better. Also click on potion symbol to access all the potions you have, but you have to click it for the corresponding character to heal them.
Also near top right is option to set your secondary skills. I set the human to lockpicking and skills can be upgraded via vendors to either add new skills, or in essence increase the max level your skills can get to. If you skip one of the imps, it may not let you get skills to +10 as the imp allows. (Thief skills like pickpocket, sneak, lockpick, etc) I would make sure to talk to him and get enough money for atleast lockpick 10)
The torture chamber master seems impossible. Just backtrack after getting some keys to the burning area that you started at where you first meet the death knight. There should be a small bow in top left area beyond previously locked gate. In battle press space much like dragonage origins, and make sure to click select all and then click enemy and unpause. I control the deathknight to hold aggro and have human archer stay back. Your bow will eventually break, but as soon as you can warp back to base camp from the key you can buy repair skill up to level 6, drag the basecamp key into your inventory and topright skill menu, you will see ability to warp to battlefield, which is an area with many shops but also areas to level up at. Skeletons won't level you up so skip the long dungeon full of them. Once you get a little further where you fight deathknights in chambers, you will soon find another battlegrounds upgrade to lvl 2.
You can now access new dungeons around lvl 7 area (Keep crossing bridges to the right of battlegrounds to reach these crystal staircase like places) You can only reach the new ones as you get higher level battleground keys.
Look for levers around, hold ALT to see items. Make sure to find a large key that allows you to travel to battlegrounds.
SEE ISN'T IT EASY TO FIGURE OUT_ OF COURSE IT IS! I recommend playing divine divinity first, i got to lv33 in divine divinity, and want to play through both of these before i get into divinity original sin further. Great game, but not as good as divine divinity, but it feels like an accomplishment to get into this game and overcome the learning curves, to get a new experience much like the previous game, but with gameplay that reminds me a bit of dragonage origins.