I'd consider cutting red entirely for a set of Sign in Blood/Night's Whisper, possibly still running martyr of sands, using black for cardraw to maintain the value of martyr. Although with all the token tools, an aristocrats package might work too.

I like the idea of making sisters super card advantagy and grindy. Something like Thoughtpicker Witch serving as a lock peice alongside some 1 drop spam and graveyard recursion perhaps, with ranger of eos keeping it running.

Still, I'll be interested in seeing what you come up with, black has some interesting tools like Plunge into Darkness, Arguel's Blood Fast  ^Flip, Athreos, God of Passage, Garza's Assassin and Profane Command.

I think red is what keeps this deck competitive. It gives me Blood Moon in the sideboard as well as a way to close out the game. Purphoros, God of the Forge does some serious work with all the tokens that will be entering, not to mention Norin the Wary gaining life and pumping our Champion of the Parish and Thalia's Lieutenant.

I was thinking of adding a Painful Truths for some more draw. I do really like the idea of Thoughtpicker Witch and might have to playtest that angle.

Thanks for the thoughts!