While sneaking past the DK patrols will work, it should not be too difficult to kill them (you may want to wait until you level up or get better equipment). In that area, I found having my archer (set to aggressive to start attacking as soon as a patrol showed up) follow behind the DK helped. I advanced the characters separately, to better control their location and spacing.
It may help if you repeatedly enter the BF and check the merchants for better weapons and armour. Also, check your stats. If your agility is low you will have a hard time hitting them and avoiding their attacks. If your survival and speed are low, they will tend to hit you first and more frequently.
BTW, the level 2 BF key can be found early in the citadel, so with a little bit of sneaking you can get access to another dungeon to level up and maybe loot some better equipment. <span class='standouttext'>Spoiler : </span><span class='spoiler'>After entering the patrol area, take the first 2 right hand turns, then enter a storage room...</span> (highlight the text to read)
In case it is not DK Patrols you are having problems with;
Just past the hanging skeletons there is a room with a (6 sided) pentagram on the ground and 6 smaller rooms, each containing a lever. If you pull the levers in the correct order, no gargoyles will appear and you will not have to fight the earth elemental. The clue for this can be found in the book just before there: "In a row, like the water flow". Water flows from high to low...
<span class='standouttext'>Spoiler : </span><span class='spoiler'>Pull the lever in the north east room, and then continue in a clockwise direction.</span> (highlight the text to read)