I haven't read The Siren Depths yet so this is based on The Serpent Sea. Basically a few warriors become consorts and a new queen arrives.
Progenitors are not birthed evil. Nothing is. It's what happens after that gradually makes them so. (Subject to additions if anyone likes it.)
Before Moon arrived at Indigo Cloud Court, the consort bower had been empty for some years and the court as a whole slowly dying. Something had to change. The three consorts of Indigo Cloud (Stone, Moon, and Ember) had had very different expectations, but the reality surprised each of them.