There is a final book published just a few years ago called the Pharos Gate if you’d care to have something like closure on this enigmatic couple. Griffin and Sabine has been a a hugely impactful book series on me.

“Yr anger is a ) rightful river & yr fear-owl a worthy adversary following above. But every being is , cursed : wearing some deathly wreath. That you feel it ; round yr neck so young is a sorry tale but one in which you join the line of Seers—you see the truth stripped bare & so the wind stings the bareness with an extra fury & so you are roped strong with that fury & that sting, the curse is there for you, bared, to bow down to & harness & wear.”

― Taisia Kitaiskaia, Ask Baba Yaga: Otherworldly Advice for Everyday Troubles