We can do our ocs in an angel and demon au!

But here is my canon character version of the au!

And as far as angel and demons, maybe Luz is a demon but she's very good and pure because she was raised outside of hell. Eda is a witch still and visited hell maybe to deliver potions or do something magic related, maybe even steal stuff or scavenge for special ingredients. She saw a demon child among a bunch of violence and just stole Luz because she didn't think any child, demon or not deserved to be there among all the trauma in hell and raised her as her own child. Luz grew up thinking she was a witch, and thinking she is Eda's blood daughter. Eda used magic to give Luz a streak of her hair that grows orange. Luz is quite oblivious and since some witches look less human like than others, she thinks that us the case for her. She also thinks she has wings because of her mom's curse.

Demon Luz, along with her Streak of orange hair, has small horns on her forehead and two black feathery wings.

Amity is an angel, like an angel princess, her family is very high status. The Blights don't even like witches that much, and of course not demons and Anity is forbidden to associate with anyone else but Angels. She's curious though about normal people and sneaks out of heaven and eventually meets Luz on the boiling isles.