The 'trouble with imps' in a Harry Potter fanfic might also be about how difficult it is to control or get rid of them. Imps are not as powerful as some other magical creatures but they are very tenacious. If they've infested a certain area of Hogwarts, like the Forbidden Forest or an old, unused classroom, it would be a headache for the teachers or the caretaker, Filch. They might try different spells to banish the imps, but the imps keep coming back, causing continuous trouble.
In a fanfic, Harry might be having trouble sleeping because he senses a new dark force approaching Hogwarts. He lies awake at night, listening for any strange noises. Ron tries to cheer him up by telling him funny stories from their previous adventures, but it doesn't really help. Eventually, they decide to explore the Forbidden Forest at night to find out what's causing his unease.
I'm not sure specifically as there could be many different takes in fanfics with this title. It might be about Harry Potter getting into all sorts of problems and troubles that are not part of the original story. Maybe he has issues with new magical creatures, or problems within Hogwarts that are unique to this fan - created narrative.
One main theme could be the complex relationships within families. In the Harry Potter universe, family is often a mix of blood relations and found families. In this fanfiction, it might explore how characters deal with family members who have different values or loyalties. For example, Harry's relationship with the Dursleys is always a point of conflict, and the fanfiction could expand on that by showing how he overcomes or continues to struggle with their mistreatment.
A fanfiction might revolve around Draco Malfoy getting into trouble for his family's actions in the wizarding world. Maybe he has to face the wrath of other students or the Hogwarts staff because of his father's allegiance to Voldemort. This could lead to a story of Draco trying to redeem himself or find a way to clear his family's name.
They might face a powerful dark wizard. In fanfiction, there are often new villains created. This new dark wizard could be after something they have, like an ancient magical artifact that Harry and Ginny are protecting.
Harry Potter is bound to be one of the main characters. Since it's about 'double trouble', there could be a version of Harry that is different in some way, like an evil Harry or a Harry from an alternate dimension. Ron and Hermione would be there to support the real Harry. Dumbledore might also play a significant role as he often has the wisdom to deal with complex situations. And, of course, Voldemort could be a central figure as well, as he is the main antagonist in the Harry Potter series and any double trouble might be related to the battle against him.
They might use their combined magical skills. Harry is known for his powerful Patronus charm, and Ginny is a very talented witch. They could use these skills to fight off whatever is causing the trouble.
One common 'kitty trouble' could be when a magical cat, like Crookshanks, causes mischief in Hogwarts. For example, it might steal potions ingredients from the classroom, leading to chaos as students and teachers try to find them. Another scenario could be a cat getting into a restricted area of the castle and accidentally activating some magical defenses.
You can try looking on some popular fanfic websites like FanFiction.net or Archive of Our Own. These platforms have a large collection of Harry Potter fanfics, so there's a good chance you'll find it there.