If you haven’t already, you might want to check out the author’s tumblr! There’s a tag for asks about the Dragon Racer characters! There are also portraits of the ROs to be found.
Also, the author has written a couple of nsfw stories for some of the characters (Shader and Cassius, not sure about the others right now) and released them on Patreon. You have to be a Patron to get access to them though. One of the stories is actually an interactive romance story for Shader in “what if” scenario where Aleyn and Shader didn’t meet at the Marauders but grew up together on the streets.