Is there a list of the different Houses in Coryani, including a description of what they are?

The short answer is no.

There are all the major val families. And their "vassal" families. Some of the ones we know of in Coryan include the Gracchi and the Voucis (allied to the val Assante), the Balin family which has ties to the VAL Tensen, the Dovitoni family which has ties to the VAL Sheen and the disgraced Otrecho family formerly attached to the val Dellenov. None of them really has the overall reputation you seem to be looking for.

In the Western lands there is a creepy family known as the VAL Baucisz ... they serve as Viceroys for the Coryani interests in the Western lands and are exactly the creepy slave holders who are into alchelmical experimentation you seem to be looking for. you could simply make up a minor branch of Coryani patricians who serve this family's interest in Coryan. That might be a very good fit.