Harry could be more empathetic. Since Remus has faced so much discrimination as a werewolf, Harry would grow up understanding the pain of being an outcast. This would make him more sensitive to the feelings of others, like the house - elves or other marginalized groups in the wizarding world. Also, Sirius's loyalty to his friends would make Harry value friendship even more deeply.
His magical abilities might develop differently. Sirius was a very talented wizard, and Remus was highly educated. They could train Harry in different areas of magic. He might be better at defensive magic earlier on, as Sirius was excellent at dueling. And his knowledge of ancient magic or magical creatures could be more extensive due to Remus's influence.
He'd probably be more confident. With Sirius and Remus as his guardians, he'd have two strong male figures who believe in him wholeheartedly. Sirius's boldness and Remus's wisdom would rub off on him. He might be less hesitant in taking risks and more assertive in his actions.
Harry would probably be more rebellious. Remus and Sirius are not exactly the rule - following types. They've both had run - ins with the law in the wizarding world. So Harry would grow up seeing that sometimes breaking the rules is necessary for doing what's right. He might be less hesitant to take matters into his own hands.
His sense of humor would likely be different. Sirius has a bit of a mischievous streak, and Harry would pick up on that. He might be more prone to making jokes and playing pranks in a more light - hearted way compared to the somewhat more reserved Harry we know from the original story. Also, Harry would be more trusting of others in general, especially those in the wizarding world, as Sirius would introduce him to a more positive side of it from the start.
His Hogwarts experience would be very different. Firstly, he would likely enter Hogwarts with a much higher level of magical knowledge. James and Sirius could have taught him a great deal before he started school. So, he might be ahead in classes like Transfiguration and Defense Against the Dark Arts. Secondly, his social status would be different. Everyone would know he is the son of James Potter, a popular and talented wizard. This could lead to him being more of a center of attention, and he might have a different group of friends. Instead of Ron and Hermione at first, he could befriend students from more well - known wizarding families.
One possible plot could be that Harry grows up with a stronger sense of family. Sirius and Remus would teach him about his parents more directly. He might be more confident in his magic earlier, as they could start his training sooner. Also, he'd likely have a different view of werewolves and Animagi from an early age.
Harry's personality would develop in a very different way. Growing up with Sirius and Remus, he'd be constantly surrounded by tales of the Marauders. This would make him more mischievous in a good way. He'd have a better understanding of the grey areas in life, as Sirius has a bit of a wild side and Remus has his own struggles. Harry would also be more independent, as Sirius and Remus would encourage him to think for himself and not blindly follow rules. He'd be more likely to question authority, especially when it seems unjust. And his sense of humor would be more developed, as Sirius is known for his jokes and pranks. Overall, he'd be a more well - rounded and confident young wizard.
He might be more traditional in his magic use as his grandparents would likely teach him older spells. Also, he could be more family - oriented since he was raised by family. He might be less impulsive as his grandparents could have instilled more patience in him.
He might be more reserved and empathetic. Remus is a rather quiet and introspective character, and Harry would likely pick up on those traits. He'd be more understanding of those with differences, like werewolves, given Lupin's condition.
He'd probably be more confident. Growing up with Lily, he'd have a strong female role model. He'd likely be more in touch with his emotions as Lily would encourage him to express himself. Also, his magical abilities might be more refined from an early age as Lily could start teaching him basic magic earlier than he learned in the original story.
If Harry was raised by Sirius, his personality would be more rebellious. Sirius was always against the traditional ways of the wizarding world. Harry would be influenced by this and might question authority more often. Also, he would be more confident as Sirius would encourage him to be himself and use his talents. Harry would grow up with a stronger sense of self - worth, knowing that he was loved and supported by Sirius.
One key plot element could be Harry growing up with a different set of values. Remus and Sirius, being outcasts themselves, might teach Harry to question authority more. He'd likely be more in tune with the magical world's underbelly from an early age. Also, his relationship with Hogwarts could be different. Instead of the sense of wonder and discovery as in the original, he might approach it with a more jaded view, having heard stories from Remus and Sirius about their own school days.