I didn't get any of this from my playthrough.. how did you find it out?
If you use the speak to the dead spell on the dead corpse inside the house, you understand they are not the good guys in the story. But it's not straightforward. I even posted something about it before some players pointed out a way to know more about what's going on.
I did cast it on several of the dead bodies but got nothing conclusive. One of them even said it was gnolls who killed him, which fits the version the paladins tell me
if you ask the dead guy how they managed to take so many gnolls he says "the pact", to which you can respond "you made a pact with a devil?", and he says "zariel".
Then you can confront the quest giver about it.
So there's a lot he says that's true but he isn't giving the whole story. They were attacked by gnolls, but it's not necessarily true that it was at the behest of Karlach. She is a fiend, but isn't necessarily killing innocents. He does have a paladin sword that he'll give you. He is a follower of Tyr (or at least, used to be), but the reason they're wanting to kill Karlach is because they made a pact with a devil out after not getting their prayers answered by their god and the devil wants her former employee returned to her in exchange for getting out of the pact.
If anything, Wyll should probably sympathize with these guys and he's kind of in the same boat.
