*puts on tinfoil hat* The Winter/Summer could have started in a way that had nothing to do with the courts. If you look back to the old Olympian myths and Skin Game when Hades got hitched Hecate(hint hint) distracts mother in law Demeter so Persephone and him can be left in peace. Now then, we've got Hecate *cough mother winter cough* and the goddess of the summer and fertility together. Another part of the myth is when Persephone spent time away from Demeter, Demeter got sad and this is what causes winter. Maybe, rather than this causing the actual seasons this was the beginning of what would eventually become the courts.
Maybe, back when the gods stepped down from defending the Outer Gates they created the Shide (crossing wildfae, mortals, and maybe an Olympian) to be their new partly mortal foot soldiers who would not be effected by the waning beliefs of mortals as the gods were. Then, Hecate and Demeter were put in charge of them which created the Courts.
Though Hestia, another one of the twelve Olympians who was the goddess of the hearth, fire, and eldest of them could also be Mother Summer.