I couldn't help but notice some hypocricy there.
When joining DB, Legion, Stormcloaks, TG, or doing any of the Daedric quests, you're "just following orders". Do you drown or jump your own character to death, too?

The only good answer here is killing Astrid. Having met the 3 victims in a different scenery, they might not have behaved the way they did (intimidation being one).
Astrid poisoning/kidnapping you, then making you face a moral dilemma.. As someone stated earlier, she threatens you and then gives you a weapon, eod.

just yesterday i tried killing astrid. it started a very lame questline.

so i reloaded the save and killed all 3 hostages like usual.

the DB questline is a lot more fun.

I killed the woman both times.

You can kill Astrid? Won't that stop you from joining the DB? Or does someone else take her place??

Yep. Thank goddess. Means I get to wipe the DB entire....

And use them as thralls, as some of them make good decor.

Um. No.