Yes that one is a common problem for most, what you need to do is the following.
1. when you get to the 2 doors with levers you need to split your team and send one into the room pull the lever with the other one. Then the next one can slip through to the next room and use the lever there.
2. When you are in the room you get to the locked door with the bony monster. Next to the door there is a torch. Blow it out and the door will unlock.
3. Kill the bugger and use the lever trick to get out again and you are home free
