The Weasleys are very common. Given their big hearted nature and their closeness to Harry in the original story, it makes sense for them to adopt him in fanfiction. They already treat him like family, so it's a natural fit.
Another character could be Remus Lupin. As one of his father's friends, Lupin might adopt Harry. He could teach Harry a lot about his parents and also about dealing with the difficulties of being a wizard, especially considering Lupin's own struggles with his werewolf condition.
Ron could also be there. He might be a bit jealous at first if Harry's adopted family is wealthier or has more influence in the wizarding world. But later, he would support Harry as always.
Obviously, Harry Potter himself is a central character. Hermione and Ron might also play important roles. They could be trying to figure out what happened to Harry and how to reverse the deaging. Dumbledore might also be involved, perhaps guiding the situation from the shadows or trying to protect Harry in his new situation.
Harry Potter himself can be a common character in such fanfiction. Maybe in these stories, he has an adopted sibling or a new family member through adoption, which changes the dynamics of his relationships. For example, if he has an adopted Muggle - born sister, he might have to protect her more fiercely from the Death Eaters.
Hermione would be a common character. She would likely be very determined to find Harry and bring him back. She might use her vast knowledge of magic and research skills to track him down.
Dumbledore could make an appearance in the form of a guiding spirit or through memories. His wisdom could be crucial for Harry as he navigates the new situations outside of town.
Obviously, Harry Potter himself is the central character. His friends like Ron Weasley and Hermione Granger are also often involved. They might try to visit him while he's grounded or come up with plans to get him out of being grounded. Dumbledore could also play a role, either as the one who enforces the grounding in some cases or as the one who might offer some wisdom to Harry during his time of confinement.
Hermione is often a key character. She might stand by Harry's side, using her intelligence and loyalty to help him through the tough times. She could be the one to encourage him to keep going and not let the disownment break him.
Obviously, Harry Potter himself is the central character as he's the one getting the wish. Hermione and Ron are also commonly involved. They are Harry's best friends, so they would be there to support him or perhaps even influence his wish. Dumbledore also often shows up in these fanfictions. As the wise headmaster, he might guide Harry on how to use his wish wisely or warn him of the consequences.
Harry is the central character as the one being adopted. The Castle family members, such as the parents in the family, are main characters too. There could also be other family members like siblings or grandparents who interact a lot with Harry and shape his new life in this fanfiction world.
Harry is the central figure, but there might be a leader in Zeltech who plays a major role in the story. This leader could be a wise and powerful figure who sees something special in Harry. There could also be other young members of Zeltech who become Harry's friends or rivals as he adjusts to his new life.