Definitely not. The two are separate entities. 'Harry Potter' has its own rich lore that has been developed over a series of books and movies. It has a very specific magic system, a detailed history of the wizarding world, and a large cast of characters with their own arcs. 'Charmed' also has its own storylines that revolve around the sisters' battles against demons and their use of witchcraft in a more modern - day San Francisco setting. There's no way 'Harry Potter' could be the source for 'Charmed' fanfiction as they are not related in that way.
No. 'Harry Potter' and 'Charmed' are two distinct fictional universes with their own unique storylines, characters, and concepts. 'Harry Potter' was created by J.K. Rowling and is centered around a wizarding world with Hogwarts School of Witchcraft and Wizardry, magic spells like Avada Kedavra, and characters such as Harry, Hermione, and Ron. 'Charmed', on the other hand, focuses on the Halliwell sisters and their powers as witches in a different magical context. They have no such source - fanfiction relationship as they exist independently.
No. While both 'Harry Potter' and 'Charmed' deal with magic, they are completely different in terms of plot, character, and setting. 'Harry Potter' is set in a mainly British wizarding world with a focus on the fight against the dark wizard Voldemort. 'Charmed' is set in the United States and is about three sisters using their powers to protect the world from evil. Their differences are so vast that it's impossible for 'Harry Potter' to be the source of 'Charmed' fanfiction.