I had to go back and check. The brother, Cain is the one that actually beheads Aria in the original timeline (Chapter 1, if anyone else wants to look). While sanctimoniously preaching "it's for your own good, now you can no longer sin". Then lets his sister Mielle taunt her, before personally taking her head off. Big yikes, no wonder Aria is so creeped out by this hypocrite.
Thank you for the translations!