Here's why:
* Siblings: The movie follows Lewis Barnavelt, a young boy who goes to live with his eccentric uncle after his parents' death. He finds out that his uncle has a secret world of magic, and he has to learn the secrets of the magic world to fulfill a prophecy. While there isn't a "family business" in the traditional sense, the movie focuses on Lewis learning magic skills from his uncle, which is a central theme.
* Family business: The "family business" in this case is the legacy of magic and the responsibility that comes with it. Lewis must learn the skills of his uncle to save the world from a dark force.
* Father's will: Lewis's journey is also about his relationship with his father and learning his father's secrets through his uncle.
While there isn't a will in the traditional sense, Lewis must prove himself worthy of the family legacy to fulfill his father's wishes.
It's possible you're thinking of another film, but this one fits your description quite well.