I cast Raise Dead! Sorry for the thread necromancy, but this still comes up relatively high on search engines when entering "sutton farm bg3" and probably a few other keywords.
That's no problem at all. I belong to a generation where the rule was not to open dozens of threads on the same topic, but instead to stick to one thread for the sake of context. With that in mind, thank you for your additional information.
Canonically, the only way to save the brothers is to side with Ethel during the initial confrontation, and then knock them out with non-lethal attacks. This opens up a dialogue option when you later talk to Ethel and Mayrina in the teahouse, where you can tell Mayrina that you fought her brothers but didn't kill them.
Have you tried this approach yet and encountered the brothers again later in Act 3? Or did Ethel's Redcaps get them anyway?
