I wouldn't count Lamia/Medusa as a Spoken, not until we see how she is down there in the coil.
The reason is simply because she is in coil, up to now everything we've seen in coil has been allagan constructs of some form or shape, from dark matter clones to AI cores to-
Well, there's Twintania and the Scourges of Meracydia, which are honest-to-god bound dragons, yet the snakes certainly looked artificial constructs.

There is a high possibility that Lamia might be a higher form of cyborg, so I wouldn't put clearly as spoken just yet.
As for Diabolos, I think he is most likely a voidsent? I mean, his aesthetic/style seems to call for being a voidsent, it's unlikely he is a Primal, same way that Siren isn't (she merely can cast charm, and is a necromancer).