I'm stuck in Dragon age 2. Please help?

I made it all the way to act 3 and im on the "Last Straw" mission. Im on my way to the Gallows and im stuck near the docks. There is a mage that summons this beast called Pride Demon and 12 shadows. No matter what method I try my companions keep dying because they get overwhelmed by all of the shadows and when my team is dead the shadows focus their attention on me. Me vs. 12 shadows and this Pride demon= instant failure. This seems hopeless. i didn't come all of the way to the end of this game just to quit. Someone please help. P.S. Running around dodging in order to use potions and revives is not working either.