I like this idea. I will admit that bringing up the three goddesses idea seemed to distract from my original idea a bit (tying in the Mothers to the Fates), but if instead the three Fates are some combination of traits from each of the various Queens (Mother Winter's malice, Titania's motheriness, and the Ladies' youthfulness), that would clear up the issue.
I also admit that I saw Mother Summer and Winter interacting a bit like Granny Weatherwax and Nanny Ogg (from Discworld) in my head.
However, that begs the question of how the Mothers came to be in the first place. We know Mab was mortal once and a WoJ suggests she got her power via an ascension ritual. But Mother Winter has never stepped down (while Mother Summer did, which is another interesting topic in and of itself), so Mother Winter must have either existed before and took up a new role or was mortal herself.