I suspect that the interrelationships of the Denarian’s are far more complex than we have been shown to date why else would such care be taken to hide information about them?
Namshiel appears to have thrown in his lot with Marcone, less than happy with Nick, we know that there are also a hidden faction working with the Black Council that worries Nick, Lasciel is suddenly interested in her child with Harry and willing to make an alliance but not out of obeisance to Nick, out of necessity.
Nick’s power over the Denarians is at its weakest in 2,000 years, so we may see more a mere two books after Next Book. We may find out who was the Denarian on the Black Council (I call Tessa, it will hurt Nick the most, and he had little control over her, I think Nick kept Namshiel on a very tight reign, his speech was archaic suggesting Nick put him in cold storage when he didn’t need him for big magic )