@alacaelum
liam and philomena do make sense, though I felt like it
was possible neither killed since Liam left his house , and philomena's job was spying not killing (though I agree spying could easily lead to killing).
lucy is the one I
really didn't expect since her family was killed 8 years ago (so she's around 7~9?) and her family's specialty was making/copying/binding grimoires - not really something that would lead her to kill anyone. I really doubt seth was cruel enough to let his kid sister do something like killing after he became her guardian.