A possible plotline is that the twin was separated from Harry at birth for some mysterious reason. Maybe a dark wizard wanted to use the twin's power for his own evil purposes. Years later, when they meet at Hogwarts, they don't recognize each other at first. But as they start to get to know each other, they sense a strange connection. This discovery could then lead to a journey of uncovering their past and their true family history. Along the way, they would face many challenges together, both from within the school and from the outside forces that are still interested in the twin's power.
One interesting plotline could be the twins getting involved in a time - traveling adventure within the wizarding world. They might use their signature prank - skills to outwit dark wizards in different eras.
Well, a cool plotline could be that the twin brother has a relationship with a character that Harry doesn't really interact with much in the original series. Say, he becomes friends with a Slytherin who has a different view on the wizarding world. This friendship could bridge the gap between the houses in a way that Harry's relationships in the original story don't. It could also lead to the twin brother having a different perspective on the ongoing conflict between good and evil in the wizarding world.
One interesting plotline could be the twin sister having a unique magical ability that Harry doesn't. For example, she might be able to communicate with magical creatures in a way no one else can. This could lead to her getting involved in adventures that are separate from Harry's at Hogwarts, but still end up being connected in some way, like when she discovers a secret about a creature that is related to a dark wizard who is also after Harry.
One interesting plotline could be the twin sister using her unique bond with Harry to help him in his battles against Voldemort in ways that others can't. For example, she might have a special magical ability that is only enhanced by their twin connection.
One interesting plotline could be the twin sister having a special magical ability that Harry doesn't. For example, she might be able to communicate with magical creatures in a way no one else can. This could lead to her getting involved in adventures that help Harry in his fight against Voldemort in a different way than in the original books.
One possible plotline could be the constant bickering between Harry and his twin which adds a new layer of family drama to the wizarding world. For example, they might compete for attention at Hogwarts, creating humorous situations in the classroom or during Quidditch matches.
One interesting plotline could be the twin sister having hidden magical powers that are different from Harry's. For example, she might have an affinity for ancient spells that have been long forgotten in the wizarding world. Another could be that she was separated from Harry at birth due to a prophecy that the dark forces were after her specifically, and she grows up in a different magical community, unaware of her true identity until later in the story.
One interesting plotline could be the younger twin having a unique magical ability that even Harry Potter doesn't possess. For example, the ability to communicate with magical creatures on a deeper level.
A great plot could be centered around their relationship with their parents. Since Harry had a difficult childhood, he might be overprotective of his sons. The twins could struggle with this overprotection while also trying to make a name for themselves at Hogwarts. Also, they could be involved in a mystery related to the Dark Arts that resurfaces, and they use their combined skills to solve it, all while dealing with the pressures of being Harry Potter's sons.
One possible plotline could be Harry having to find creative ways to get by without money. For example, he might barter his magical skills for goods and services. He could offer to help with spellcasting in exchange for food or school supplies.