Hermione would be heartbroken. She would probably try to find out the exact cause of Harry's death, suspecting the Dursleys' negligence or worse. Ron would be furious with the Dursleys and would want justice. Dumbledore would be deeply saddened as he had placed so much hope in Harry. The Weasley family would also be in mourning, having considered Harry as one of their own. And Voldemort would be triumphant, thinking that his greatest obstacle was removed.
The wizarding world would likely be in shock. Harry was seen as a hero, and this act would completely change their perception of him. Some might think he was finally getting revenge for all the abuse he endured, but many would condemn his actions as murder is still a serious crime in the wizarding world.
Percy would likely be very critical of their lifestyle. He comes from a world where family is important and they support each other in the face of danger. The Dursleys, on the other hand, seem to shun anything out of the ordinary and are unkind to Harry. Percy might try to show them a different way of living, with more love and acceptance, though they probably wouldn't listen.
They would probably be horrified. The Dursleys have always despised magic and those associated with it. Teddy, being a young wizard, would represent everything they dislike. They might try to shoo him away or call the police, thinking he's some sort of freak.
They would likely be disgusted. The Dursleys are so anti - magic that any form of fan - created stories about the magical world would be abhorrent to them.
The Dursleys' reaction would be complex. Vernon would be enraged and might even try to burn any fanfiction he found. Petunia would be conflicted. Part of her would be disgusted, but a small part might be a bit curious as she has some connection to the wizarding world through Lily. Dudley might be more interested than his parents, especially if the fanfiction had some action or adventure that appealed to his more adventurous side.
They would be devastated. Harry has many friends and allies. People like Hermione and Ron would be heartbroken and would probably seek revenge. The Hogwarts faculty would also be deeply affected. Dumbledore, if he's still alive in the fanfiction, would feel a great sense of guilt for not protecting Harry better. There might be a split in the wizarding community, some believing the Dursleys were acting on their own, others suspecting a darker conspiracy.
The Dursleys would most likely be horrified. They have a deep - seated hatred and fear of magic, and Ron and Hermione are clear representatives of the magical world. Vernon might turn red in the face and start shouting, while Petunia would clutch her pearls and Dudley would cower behind them.
They'd probably be horrified. The Dursleys are very much against the idea of magic, and fanfiction might introduce even wilder ideas about the wizarding world.
They might be terrified. The Dursleys are used to a normal, non - magical world, and Harry's family is full of magic. They could see something as simple as a wizard apparating and completely freak out.