I'm not sure how taking over the father's toy factory will prove that the brother is delusional, Andy Silverman.

I think it's close. Just food for thought/workshop ideas: "When a priggish man discovers that his man-child brother still believes their father is Santa Claus, he makes it his mission to prove his brother wrong, but discovers something magical that could alter his beliefs forever." Not suggesting this is better, just another angle.

Thanks Derek, That's good. I'll tweak it a bit but I like it better than what I had.