What I find pretty stunning is that Harry summoned(or encountered, in the case of the mother summer) all of the senior powers of faerie in a very short period of time. Bro goes hard. Also, mother winter is a stone cold boss. She is most definitely the scariest queen.

I got the impression reading this book that Mother Summer and Mother Winter were actually the same person, or at least two sides of the same coin.  After all, Mab and Titania are sisters, as Aurora and Maeve are cousins.  Unless there is some big bad daddy figure we don't know about, the two queens must have the same mother.  Considering that the Sidhe courts seem to be all about feminine power, I doubt that their mantles of Queen were passed down from their fathers.