The teachers at Hogwarts, like Professor McGonagall, would likely be a bit taken aback at first. Fanfiction often takes liberties with the established rules and norms of the school. However, she might also recognize the passion of the fans and see it as a testament to the impact of Hogwarts on their lives. She might secretly hope that the fanfictions didn't give students too many wild ideas about breaking school rules.
Luna would be very open - minded. She might see the fanfiction as just another form of magical thinking. She could find the wild and imaginative ideas in the fanfictions quite endearing and might even start to incorporate some of the concepts into her own unique view of the wizarding world.
Harry Potter might be a bit surprised. He'd probably think it's strange that people are writing about his friends' and his own relationships in such a different way. Hermione would likely be very interested in the writing style and how the authors are creating these new relationships. She might even take notes to improve her own writing. Ron would just laugh it off most of the time. He'd find it a bit odd but also funny.
Hermione would probably be devastated. She was Harry's closest friend and ally. She might be filled with rage towards Vernon and vow to seek justice. Ron would also be heartbroken and might want to take matters into his own hands against Vernon.
She would probably be furious at first. Harry is known for her strong will, and being forced into a marriage, especially with Draco, would go against everything she believes in. She might try to fight it directly, using her magic skills to break free from whatever is forcing this marriage.
They could also be offended. If the fanfiction portrays them in a way that goes against their values or character traits in the original work, they may feel misrepresented. For example, if a character is always shown as noble in the original but is made into a villain in the fanfiction. They might not like this change at all and feel insulted.
They might be amused. Since fanfiction often contains creative and sometimes humorous takes on the original story, characters could find it funny to see how fans imagine different scenarios for them.
They could also be confused. If the fanfiction takes a really wild turn from the original story, characters might not understand the new concepts or relationships presented. For example, if a fanfiction pairs two characters who have no interaction in the original in a romantic way, it could be bewildering for them.
They may also be confused. Fanfictions often take the original story in new directions, and characters might not understand why certain things are written the way they are. For example, if a fanfiction changes the relationship dynamics between characters, they could be left scratching their heads.
They might be amused. Some characters could find the creative interpretations in the fanfiction quite interesting and it might make them laugh or at least bring a smile to their faces.
Some frozen characters could be amused. Imagine Elsa from Frozen reading a fanfiction where she has a new adventure in a different kingdom. The creative ideas in the fanfiction might make her laugh or at least find it interesting.
They might be really amused. James could find it funny to see different takes on his family's story. Lily might enjoy seeing new interpretations of the magical world she was a part of. Albus could be intrigued by how others view his father's adventures.