Hermione would probably be there. She might be helping Harry prepare for the test, giving him tips on how to answer different types of magical questions. Another could be Ron, providing moral support and some comic relief during the tense time of the test.
Dumbledore could be a key character. He might have some special interest in Harry's performance in the magical aptitude test. Maybe he has a plan for Harry depending on the results. Also, Professor McGonagall could be involved, as she often oversees students' academic progress at Hogwarts, and the test is an important part of that.
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.
In this fanfic, perhaps Harry discovers he has a unique magical ability during the test that no one expected. It could lead to him getting special training or being involved in a secret mission related to his newfound talent.
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.
Hermione could be there. She's always around to support Harry and might be observing the ability test.
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.
Well, Gandalf would probably be a main character too. He is a powerful wizard in Middle - earth and his knowledge and guidance would be crucial in a story where Harry is involved. He could be the one to help Harry understand the differences between his magic and the magic of Middle - earth. Also, Aragorn could be part of it. His leadership and warrior skills could be something that Harry looks up to or tries to learn from in this fanfic.
Obviously, Harry would be one of the main characters.
Snape could also be part of it. He might catch Harry in a rather awkward moment when he's trying to hold it in and give him a hard time. Or, on the other hand, he could surprisingly offer some help in a very Snape - like way.
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.
Hermione would surely be one. She's smart and would be great at helping with the academic side of building a school, like creating the curriculum.