Sending a kid with every reason in the world to hate you and who has great talent in magic to the most prestigious magical school in the world seems like a recipe for disaster to me.
But who knows, maybe that's just me.
@ColorlessBoy well remember there is a high causality rate at this school. Like IIRC it's 80% just in the entrance exam and the classes are even harder. SO maybe the Uncle's hoping to get the guy killed.... plus it seems the Uncle doesn't know his nephew is aware that rest of his family were murdered and not in an "accident":