[rogerpepitone]

Spoiler for Wakuseino's problems:

1: The epitaph is a riddle that describes how to find the gold / get to Kuwadorian. (From Eva's actions in ep. 3)
2: Whoever is killing, at least in episodes 1, 3, and 4, is knowingly not fully following the epitaph. (Kinzo can't be sacrificed in ep 1/3, as he is already dead. People aren't injured in the right places in ep. 4.)
3: Conclusion: The killer is trying to convince somebody that the ritual is being followed and Beatrice is revived; only Maria makes sense at the dupe.

In ep. 4, I think that somebody else is running the tests that the cousins take. (Probably Genji & Nanjo executing Kinzo's true last will & testament.) Nobody is being harmed during those test; everybody who they talk to on the phone is in on it. The killer feared that the reveal at the end would spoil the whole "con Maria into telling / doing something" plan.

But because s/he had to rush things, the job wasn't carried out well, and Maria realized that "Beatrice" had been fooling her the entire time. She killed Beatrice.

Battler's sin was that 6 years ago, he'd planted the seeds that caused Maria to believe in witches, and after being disillusioned, she realized all that. When he didn't understand, she grew depressed and took poison.

No idea how Battler died, though.