The battlefield entry in the main menu is for the after game BF.
The DK patrols were weakened quite a bit from what was originally planned, so you should not have too much trouble killing them. You can sneak past them, or sneak close, attack with a bow and withdraw out of range to attack again. I just had my warrior out front, with the archer character behind set to aggressive, to attack as soon as a DK patrol showed up. I moved each character separately, to keep the archer out of harms way.
