I just left West Harbor, arrived at Weeping Willow. Fought at Khelgar's side. Cut scene put us inside and the enemy attacked. We dispatched those on the first floor. Went upstairs to deal with the next lot.

I got swarmed and died within seconds. Repeatedly. With different characters. I've tried a Favored Soul-- complete wash. Now with a Swashbuckler. Same result. Am I doing something wrong? Is there a tactic I should be using?

I know I played this campaign years ago, and I know I got past this point. So what's happening this time?

I know this is a late reply but... You can leave your main character behind and let Khelgar do most of the work. Give a general hold command and simply butcher them with Khelgar. You are probably past that point by now since that floor is very easy once you get the hang of the game. :P

Heh. My reply is a great deal later but here goes because I remember it.
It turned out that I was forgetting to equip Khelgar. He was going into battle with his bare fists. Naturally he died quickly.

Later when I did things properly the Weeping Willow turned out to be easy.

And to be fair that fight upstairs at the Weeping Willow is the first one in the OC that offers any significant challenge with the way the swarm on you.