User blog comment:EmpyreanSmoke/Supernatural Q&A/@comment-95.112.212.185-20150813213020/@comment-24834479-20150819001109

Angels can use their powers because of their grace, not by it, so it wouldn't have an effect on other beings.

Reapers don't need to possess a human to exist/manifest in the veil, and so they can still fly around there like Tessa did in a couple episodes.

I'm not quite sure about this question, but as far as I know, guessing, the alternate Earth was made by the spell, and Olberon created the fairy world.