Dialogue options that didn't mean what you thought at all?
I convinced Astarion not to ascend and afterwards he asked what he should do with the vampire spawn.
I chose the option "Why not just leave them? They're not our responsibility," thinking that I was saying "let's not decide their fates right now on impulse, we should let the Gur decide what to do since their children are among the spawn." I also thought that maybe selecting that option would cause Astarion to choose their fates himself.
Instead he broke the staff and trapped them there forever... whoops. Sorry Sebastian.