Have you read the Sedumen Glossary?
Scourge of the Nephilim collects books 4-6 of The Sedumen Chronicles, along with a complete glossary of terms, into a single collection.
The Dawning of Firebird Alex collects the first three novels in The Sedumen Chronicles, along with the novelette Firebird Manor, into a single collection.
Alexandra Gold knows she's half-human, half-demon from another universe, and it terrifies her. When another from that universe starts hunting her loved ones, she has to face her fear and become Firebird Alex if she wants to survive and save them.