Dumbledore could play a crucial role. As the wise headmaster, he may have some prior knowledge about Harry's possible inheritances. He could guide Harry through the process, explaining the significance of any new powers or items he has inherited and how to use them for the greater good of the wizarding world.
Dumbledore could be involved too. He often has a deeper understanding of things in the wizarding world. He might be the one who arranges the heritage test for Harry, or at least be aware of it and offer his wisdom and guidance. Also, some of Harry's professors could be involved. For example, Professor McGonagall might be curious about the results and how it could affect Harry's performance in school. And, there could be some characters from Harry's family's past that make an appearance, either as memories or some sort of spectral form during the test.
The teachers, such as Professor McGonagall or Professor Snape, would most likely be involved. McGonagall could be the one administering the test, while Snape might be observing with his usual critical eye. Also, other students in his year could be taking the test alongside Harry. They could be either competing with him or collaborating in some parts of the test. This would add an element of drama and friendship or rivalry to the fanfic.
Harry and Ron are likely to be involved. They are her closest friends, and they would surely be there for her during such an important event. They might offer moral support or even help her solve some of the problems related to the test.
It could be a dark wizard who wants to steal Harry's inheritance for his own gain.
In this kind of fanfiction, Harry might discover some unexpected magical inheritances. For example, he could inherit a powerful ancient magic or a special magical artifact from a long - lost relative. This new inheritance could change his status in the wizarding world and also give him new powers to fight against Voldemort or other dark forces.
Well, in such a fanfiction, Harry might discover some hidden magical powers or a special bloodline connection. It could lead to him having new allies or facing new enemies who are interested in his newfound inheritance.
It could be a new character, perhaps a young witch or wizard who has just received their Hogwarts letter and then discovers this inheritance. This would be an exciting start to their magical journey.
Hermione could be with him. She would probably be there to offer moral support and maybe even use her vast knowledge to understand the blood test better.
Ron might also be there. He could be the one who offers Harry a place to stay at his own home if Harry is having trouble finding a place. Or, if they've had an argument, Ron could be the reason Harry is moving out in the first place.
It's hard to say for sure without reading it, but likely Harry Potter himself would be a main character. He's the central figure in the original series, so it would make sense for him to be involved in an inheritance test. Hermione Granger could also be a main character as she's always been very involved in the magical mysteries.