What your people call the original inhabitants will ideally tell the reader a lot about:
1) your people
2) Their interactions with the original inhabitants
3) What happened.
So calling the original inhabitants "Natives" or "Mud-grubbers" is totally different from calling them "Demons" and is different again from calling them "The Elders".
Given that, it's hard to really know what to advise you with no clue at all about the history

If I read "The Creators" I might assume you had a really old and powerful race that made cool stuff and disappeared mysteriously, with possible but unclear links to the current people there. Cause I've seen that before

If it's different from that, the nuance of how it's different would inform the best term to use.
I'd suggest not "The Old Ones" in a fantasy series, esp a YA one, since that's pretty strongly associated with Susan Cooper's "Dark is Rising" books in a lot of heads, and shall probably be more after the (cringe-at-how-bad-it-sounds) movie.