One of the coolest things about Larian Studios is the fact that you can wander if you want and discover stuff on your own OR, take on quests like this one, which often go off into totally unexpected directions. There generally is almost ALWAYS more than one way to accomplish things in their games, and BG III is no exception.
I hate rpgs that only pretend to offer freedoms to do what you want. BG III is fantastic because there really is no "right way". This results in being able to have many playthroughs, each with memorable different things.
I bumped into Auntie at the druid camp, and she was quite friendly. While she seemed a bit odd, I missed the clues that her whole swamp wasn't quite what it seemed, and went there looking for tea and maybe a cure for my tadpole troubles. Bumped into the brothers, and it was clear trouble was afoot.
The whole episode played out sweetly until the final encounter, and Ethyl froze in place when we snuck up on her and attacked deep in her cave lair.
I assume this is a known bug?