Bill would likely experience a range of emotions. He'd be horrified at the thought of Harry being abused. His first instinct would be to comfort Harry and assure him that he's safe now. Then, he would start making plans to deal with the situation. He might contact his friends in the Order of the Phoenix to get help. He would also be thinking about how to help Harry heal from the trauma, perhaps by introducing him to some calming magical creatures or spells.
Well, Bill could be shocked at first. But then he would likely become very protective. He may take Harry to a safe place, like the Burrow, and gather his family around to support Harry. He would also probably try to find out more about the abuse, like who was behind it and for how long it had been going on. He'd be determined to make sure it never happened again.
He probably gets angry. Bill might be furious at the person who is abusing Harry and vow to protect Harry at all costs.
He might be shocked at first. Then he could feel a strong sense of protectiveness towards Harry. Maybe he immediately tries to find ways to keep Harry safe from further harm, like staying closer to him at all times.
Sirius would likely be extremely angry. He already has a protective streak towards Harry. He might immediately confront those he suspects of the abuse, whether it's the Dursleys or others at Hogwarts. He would probably also try to remove Harry from the situation as quickly as possible.
He could start teaching Harry some defensive magic in case the abuser tries to come back. Also, Bill might use his connections to find a healer or a counselor who can help Harry deal with the emotional trauma of the abuse.
Arthur might be shocked and immediately want to protect Harry. He could start by confronting those who are abusing Harry or find a safe place for Harry to stay.
Viktor might be shocked at first. He could feel a strong sense of protectiveness towards Harry. Maybe he immediately tries to comfort Harry and assure him that he's not alone anymore.
Well, Dumbledore has always had a special connection with Harry. When he finds out about the abuse, he would be devastated. His first instinct would be to comfort Harry. He might also reflect on his own actions and whether he could have prevented the abuse from happening. Dumbledore would then use all of his resources to make sure Harry is safe and happy. He could provide Harry with a mentor or a guide to help him through the difficult times, someone who can teach Harry how to cope with his past and move forward in a positive way.
Nico might be initially shocked. He could feel a deep sense of anger towards whoever was responsible for Percy's abuse. Then he would probably become very protective of Percy, vowing to keep him safe from any further harm.
Bill might be in shock at first. He couldn't believe such a terrible thing had happened to Harry. His initial reaction could be a stunned silence as he tries to process the information.
He might be filled with rage. James Potter was a loving father figure in his own right. So, when he finds out about Harry's abuse, he could immediately seek to confront the abuser. He would want to protect Harry at all costs and might use his magical skills to ensure Harry's safety.