Both Sebastian and Abigail have a "success" ending, a "failure" ending, and a "secret" ending. Secret endings are unlocked by the choices you make, but to get the chance to make those choices, you have to visit the right locations.
*light spoilers ahead, stop reading here if you want to figure it out yourself*
You'll still have to figure out the right dialogue choices to make, but here's a hint. For Sebastian, visit Cindersap on Monday, Tuesday, and Wednesday, and then Town Square on Thursday. For Abigail, visit Cindersap on Monday, Town Square on Tuesday, Cindersap on Wednesday, and Town Square on Thursday.
I posted a full walkthrough on Tiktok for Seb's ending. Hope that helps :)