The younger characters in Encanto like Antonio would be excited. He loves stories and new ideas, so Mirabel fanfiction would be like a new adventure for him. He might want to share it with his animal friends. And Dolores, with her ability to hear everything, might already know about the fanfiction. She could be either intrigued or a bit worried depending on how the fanfiction is being received by the rest of the village. If it's causing a stir, she might be concerned about the family's reputation, but if it's positive, she would likely be quietly supportive.
If the fanfiction incorporated the family's magic in new and creative ways, some characters might be delighted. For example, if it showed Mirabel having a new form of magic related to her ability to bring the family together, the family members might see it as a positive expansion of their story. However, some might be skeptical. Abuela Alma might question if it goes against the family's established magic traditions.
The Avengers would be devastated. Hawkeye, who has a sort of father - figure role in the group, might feel guilty for not being able to protect her. Captain America would be deeply affected as he values every member of the team. He would probably vow to make Ultron pay for her death. Iron Man, on the other hand, might blame himself for creating Ultron in the first place, which led to this situation.
They might be really surprised. Some characters could be flattered by the positive portrayals in the fanfiction. For example, Mirabel might be happy to see different interpretations of her story and how she's seen as a hero in some fics.
In this fanfiction, Abula and Mirabel are likely characters within a particular fictional universe. Maybe they are part of a family or a community. Without more context, it's hard to say exactly who they are, but they must have some sort of relationship where Abula has the power or authority to kick Mirabel out.
Encanto is an original story. Disney's team of writers and animators came up with the concept and brought it to life on the big screen. It's not a adaptation or retelling of another story.