We know that Mab and Titania are sisters, because in Cold Days, Titania says she hasn't spoken with her sister since before Hastings - Which causes Harry to remark on the epic scale of the dysfunction in that family.


But there's a Mother Summer and a Mother Winter.  If Mab and Titania are sisters, whose daughters are they - Summer's or Winter's?  Or was it neither, and they were adopted somehow?