Actually since I posted, I have actually beat it.
The trick is you you chain together, a whole heap of quickening, and cast Berserk on vosler, and then just attack all out.
P.S: All my characters were level 22.
Good for you. I have beat the game twice, but I have never figured out how to use the quickenings. I can never get them to work. So I just wait until I am strong enough.