Another "moral dilemma"...yawn...
Let's put this in the concrete shall we? A strange carney tells you this scenario, you're going to go report him to someone, and that's about it. Maybe if you're particularly savvy, you'll ask to see the money, then knock him out and take it - or humor him and press the button, to which nothing will happen, and you'll take money from this rich crazy person.
Anyway, this is never a 'moral dilemma'. Either you view your family member's lives as of quantifiable/commensurable worth with money, in which case a little moral calculus will tell you what to do, or you do not, and the whole proposition is absurd.