If its such a bore, just use some initiative by force attacking them and they can all be dead rather quickly.
Voila, toughness proved.
I was quite disappointed in this encounter aswell though, to be honest. I tried using all of my characters in dialogue options but could not get anything different between them other than the bland ones which were offered. Everything about the entire situation seemed to reek of 'inevitable bloodshed', which is why I ended up simply attacking them without bothering to engage in dialogue in the end, to gain the advantage.
I use this tactic regularly when I know combat is inevitable - although it has backfired a couple of times. The Throne of Bhaal thread about princess Daiyatha was the last instance. I'm not so concerned with Icewind Dale II, since it is much more combat oriented.