Wouldn’t it be funny if it were Diana or Faye and it turns out they were magically concieved. Basically, they have two biological dads (Blackwell and either Charles or Thomas) and they never had biological mothers to begin with?
Now THAT would certainly be a twist!
But realistically, I still hold firm that Diana and Faye make no sense as half-sisters unless the show pulls something really contrived out of their asses. (Yeah, watch Blackwell turn out to be a secret Meade just so Diana can be Cassie’s half-sister. Gag me!)