If I could report it as having dropped in the lap of both my brother and I equally then I would start by doing that. Then I would pack up and move out of town and get a part time job doing something I enjoy and quietly live the rest of my life.
You mean you'd need $1.5 mil for your brother, too, in order to do that?
I would set aside whatever would be needed for taxes and invest the rest before year-end.
Gamble it. Spend a month out in Vegas and play in the World Series of Poker
High roller suite at the Cosmopolitan?