Perhaps they form a secret club within Hogwarts where they plan elaborate pranks on the Slytherins. This could involve using their combined knowledge of magic and mischief to outwit their rivals in really creative ways. They might also end up uncovering some dark secrets about the Slytherin common room in the process.
One idea could be that Harry and the Weasley twins team up to play a huge prank on Snape. They use a combination of Fred and George's magical inventions and Harry's invisibility cloak to get into Snape's office and rearrange everything in a really chaotic way.
One idea could be that Harry has to team up with the Patil twins for a special magic project at Hogwarts. They discover a hidden magical artifact in the library and have to figure out how to use it without getting caught by the teachers.
One idea could be the twins inventing a new type of magical prank product that has unexpected effects on Hogwarts. For example, it might make the staircases act even more erratically than normal, causing chaos throughout the school.
Another plot idea could be that the Riddle twins have a special connection to an ancient magic that Harry and Hermione need to understand in order to defeat Voldemort once and for all. The twins could hold the key to unlocking this magic, and throughout the fanfiction, they go on a journey with Harry and Hermione to discover how to use it.
One idea could be the Patil twins using their unique magical skills, perhaps learned from a different magical culture, to help Harry in a dangerous mission. For example, they might have a special way of divination that gives Harry an edge in predicting Voldemort's moves.
One idea could be that the Carrow twins have a change of heart. Maybe they start to see the wrong in Voldemort's ways after a series of events. For example, they witness an innocent being brutally punished by Death Eaters and it makes them question their loyalty.
One idea could be that the Jackson twins have a secret power that they discover together. They then have to keep it hidden from the world while also trying to figure out how to use it for good.
Well, they could be the result of some sort of cross - over experiment gone wrong (but in a good fanfic way). Maybe they have powers from both worlds but struggle to control them at first. For example, they might accidentally cast spells while trying to use their demigod powers. And they could be the bridge between the two groups of friends. The demigods are skeptical of wizards and vice versa, but the twins help them understand each other.
One idea could be that the twins have powers from both the wizarding world and the demigod world. They can use magic spells like in Harry Potter and also have the abilities of a demigod from Percy Jackson. For example, they can control water like Percy and at the same time cast defensive spells. Another plot could be that they are sent on a mission to stop a threat that endangers both the wizarding world and the Camp Half - Blood. They have to use their combined knowledge and skills to succeed.
A great plot could be that they discover they are twins later in their Hogwarts years. This revelation could cause a stir in the wizarding world. They might then start to explore their family history together, finding out secrets about their parents that were previously unknown. Maybe they find out that their parents had some special mission that they now need to continue as twins.