There is no such thing as an atheist religion.
Dwilight especially has stricter rules for religions than other islands.
It is a religious option in the same way any other faith is
No.
The moment you start doing it, you get burned at the stake.
No atheism. Nowhere. Period. Don't like it? Too bad. Play someone else's game.
I don't like it, I don't like its historical ignorance nor do I like the fact that realms are disadvantaged by not having a state religion, I don't like how your historical education is so black and white its almost a bad joke. It would be hard, dangerous, would make a pariah out of any noble or realm that took it upon them but its certainly not imposible for athiesm or expecially agnosticism to exist in your settings. Nor will I stop reminding you of that fact when the subject arrises.