So, Ebenezer and Mab are discussing Harry and "She nodded to Ebenezar and said, “Br—”
Butcher, Jim. Battle Ground (Dresden Files) (p. 49). Penguin Publishing Group. Kindle Edition.
My current wag is that she was going to call him brother. This would give an additional reason Harry's mother was called Margaret Lefay and why Kinkaid told Harry that he was as human as Harry was.
Edit: Even though from the story so far it appears that Mab is much older then Ebenezer (so I'm not sure how that would workout) but it's still my guess.
Edit 2: It also explains why in (Winter Knight?) the Summer crone told Harry that the Winter crone liked him. It would also explain why no mention has been made of Ebenezer's wife, Harry's grandmother. Surely at some point Harry would be like "tell me about grandma." Maybe (this is kind of out there) Eb has the blackstaff because he took it from grandma when he split.