Yeah I got the path through the sewers. At the start of the battle when that mothersmurfer comes towards me I roll and run up those stairs, turn around, try to block the dogs and kill them, but by then he's also up there and just smashes me with an overhead strike.
How do I upgrade my trout? I don't think I've unlocked that option yet. So far my favourite weapon is the halberd, it kills the dogs in like 2 strikes. I think it has a better reach than the estoc with its forward stab.