Thank you, I'm so glad you're enjoying the game and that you love Aeden! :) I'm happy to answer any questions you have.
"Dun nora leew cnor" roughly translates to, "Back into your dark." A'sta translates to "go", and adding "be" just makes it a command spoken with authority, and has the impact of, "Go NOW."
As for cnamh sith, I just made it up. The bone faerie itself is based off the wendigo, but I wanted a name for it that felt like it had origins in the Night Realm. Cnamh is Irish for "bone", which is why I chose it.
Let me know if you have any other questions! :)