Yes they can very easily work in Aladdin/Jasmine, Princess and the Frog characters into a one-off; but for these particular casting calls, it’s most likely not them.
I don’t think it’s the brothers Grimm because I really believe they would have done that for the Author plot line. Its like the most obvious thing they could have done. I don’t think they’d make the storytelling more complicated by having two other corrupted authors.
This doesn’t jive, though. I mean, yes, having the Brothers Grimm during the Author plot would have made a tremendous amount of sense but its not like OUAT doesn’t re-tread already walked upon ground. They are constantly plagiarizing themselves, reusing old ideas or themes in new seasons. The Author Isaac dealt with the book and answered those questions. But, for me, the big question of how our stories are so different from what the Onceiverse has shown is still a big question and one that A and E keep saying they do want to answer…so I do think it’s the Brothers Grimm and we’re going to learn how the stories of the EF, NVL, ect ended up in our world. That’s really the final big mystery to conclude the entire series.