So, what do you think? Should we be able to keep both Karlach and the Andersons of Zariel alive?
Yes, and I rather like your soul coin solution. I only found two so far; did you find four (enough for all tollhouse residents)?
But let me redirect:
The only people who cannot lie to you are the dead. You may also get correct information out of successful Perception and Investigation rolls and the actual game evidence.
Known from the dead:
---Both tollhouse personnel were killed by gnolls.
---The dead cultist inside the tollhouse was pacted with Zariel and killed by gnolls.
---The dead cultist on the bridge with the gnolls will not speak to you. (I haven't tried the gnolls; something to try.)
Investigation roll:
---When talking to Anders, you get an Investigation roll when he describes Karlach's crimes. The roll tells you his description doesn't match known behavior for devils.
Actual evidence:
---The dead gnolls and cultist on the bridge.
---The dead gnolls outside the tollhouse. Same.
---The dead cultist in the tollhouse.
---The hacked-up bodies behind the tollhouse.
---Anders has the sword of Tyr. Note that apparently anyone can use it - even characters without proficiency can wield it long enough to activate its power. So can the vampire spawn, the clearly Lawful Evil githyanki, the cleric of Shar, the pact-sworn Wyll, etc. There are no apparent race, alignment, class, or deific restrictions on use.
I don't really expect people at Larian to set up a CSI crime scene for us to solve, but they have to have some basic understanding of the ideas and have a backstory to follow, so assume this is a crime scene, all narrators, except as noted, are unreliable, and go with the evidence.
The things that stand out to me are the body parts behind the tollhouse - they are 'hidden' (deliberately out of the way) and dismembered. There are four other gnoll attack scenes and, in two of them, the gnolls win. In those, the bodies are eviscerated and eaten, not dismembered. So gnolls didn't do it. Karlach is showing a crossbow, but she may have a bladed weapon, so she is a possibility, but there is no evidence she made it as far as the tollhouse. The tollhouse personnel have no reason to do it and there's no evidence they did. Anders has both means and opportunity; he is the only likely candidate. In this world, you destroy a body to keep Speak with Dead from working. Otherwise, he could have dropped the body near the gnolls and everyone would have believed they were killed in the fight. So it looks like Anders killed (possibly) and dismembered (likely) at least one other person. That is not the work of a paladin or a person who is trying to do good despite his pact (contrast Wyll).
Karlach's story basically holds up, although there may be elements that are lies.
Anders and company's stories do not hold up, except for the fact that they did fight the gnolls and the clear enmity with Karlach.
So my best guess is: Ander's group did fight the gnolls, but only because they were attacked. There was one remaining tollhouse employee who would have been a witness to pact power uses, so Anders took that person out back and killed and dismembered them. Even if he was a paladin, he isn't acting like one, so I am guessing the whole 'paladins of Tyr' story is based on the fact that they have the sword - perfect evidence until you realize that anyone can use it. And only a trusted servant of Zarial would be given the sword in the first place, so Anders isn't a reluctant servant.
Now that I have gone out on a limb, does anyone want to chop it off? (With evidence and logic, please.)
