>>718304152
They are really bored about being kakeraverse witches and they are the only beings who can understand each other, the only logical outcome is to become close in their own fucked up way.
But also they aren't really evil at all, if it wasn't for them Umineko ends at ep 1 with Battler giving up and that's it, then twice at ep 5 and ep 6 with Battler either still not getting Beatrice or Ange not knowing what was even her role.