Well, it would change everything. For one, Draco's attitude towards Harry might be different. He could be conflicted between his loyalty to his Slytherin friends and this newfound family connection. And Harry, he'd have to deal with the fact that he has a son who was once his enemy. The whole dynamic at Hogwarts would shift, and the battles between Gryffindor and Slytherin might take on a whole new meaning, as they are now sort of family - in a very strange way.
This fanfiction concept is really interesting. Harry being Draco's younger brother would mean a different upbringing for Harry. He'd have access to the Malfoy's wealth and status. However, his personality might still shine through. He might be a Slytherin with a heart of gold, trying to change the family's views from the inside. His relationship with Dumbledore would also be different as Dumbledore might see him as more of a 'project' to save from the Malfoy influence.
In a fanfiction where Harry is Draco's brother, it would be a wild shift in the story. The sorting ceremony might have been really interesting. Harry could have been conflicted between Gryffindor and Slytherin. His friends in Gryffindor might have been very suspicious of him at first. His relationship with Sirius would also be strange. Sirius hated the Malfoys, so would he still be as fond of Harry? And Harry's magical abilities might have been nurtured in a different way, perhaps more towards the Dark Arts, which could have made him a very different kind of wizard.
The 'snape is harry's father fanfiction' can transform the entire narrative. Harry's identity and self - discovery journey would be on a whole new path. He might not have grown up with the Dursleys if Snape was his father. Snape would have likely had different motives for his actions throughout Harry's years at Hogwarts. The relationships with his friends, like Ron and Hermione, could also be affected as they might view Harry's new family connection in different ways. It basically takes the core of the Harry Potter story and gives it a huge twist.
Well, it would likely make their relationship much more complex. Instead of the typical rivalry, there could be a sense of family obligation. Draco might feel protective of 'her' in a different way than he would a male Harry. He might be torn between his family's views and this new connection to Harry.
If Hermione and Draco were siblings in fanfiction, it would completely turn the original story on its head. For one, Hermione's Gryffindor nature and Draco's Slytherin one would create a really interesting family dynamic. Their parents must have had a very complex relationship for this to be possible. It could lead to Hermione having a different view of the wizarding world from the start. Instead of being a Muggle - born advocate in the way she was, she might have had some internal conflict due to her Slytherin - influenced family ties. And Draco might not be as much of a bully as he was originally, or at least he would have a different kind of relationship with Harry, Ron, and Hermione.
If Sirius and Remus were Harry's fathers in a fanfic, it would change a lot. For one, Harry would have two dads who are very different yet equally loving. Sirius being an Animagus and Remus a werewolf would expose Harry to a different side of the wizarding world from a young age. Also, their relationship would add a whole new layer of depth to Harry's character development as he navigates his own identity within this unique family structure.
Well, it would change a lot. For one, Draco's family would have a different connection to Harry. Instead of being rivals, they might be more protective of Harry. Draco could use his pure - blood status to shield Harry from some of the prejudice in the wizarding world. Also, the whole dynamic at Hogwarts would shift. Draco might be more like an older brother figure to Harry, guiding him in certain aspects of magic and school life, which would be very different from their original hostile relationship.
He would become more cautious. Harry has faced so much danger in his life, and as a father, he would do everything to keep his children safe. So, he might be a bit overprotective at times.
In these fanfictions, Harry may develop a more diplomatic side to his personality. Since Draco is from Slytherin and has a different way of thinking, Harry has to learn to negotiate and find middle ground. For Draco, his friendship with Harry can make him more empathetic. He might start to care about the well - being of others outside of his Slytherin clique, like the Gryffindors and other Hogwarts students, which is a big change from his initial self - centered attitude.
If Harry were Draco's older brother in this fanfiction, their relationship at Hogwarts would be a total mess - up of the original dynamic. Harry would be constantly torn between the Gryffindor values he adheres to and his family bond with Draco. Draco might start to question his Slytherin - only ideology because of his connection to Harry. For example, they might find themselves in situations where they have to choose between their house loyalties and their new - found brotherly bond, like during the Quidditch matches or the Triwizard Tournament.