Interesting decision. If it's immediate family (as in mother father siblings) I'd choose no button and take the key. Now if we wanted to get more distant, I'd be far more inclined to take the button. If there are 5 members out of my 100 member family that I really care about, thats a 5% chance one would die. But then there's Murphey's Law to take into account as well, so knowing my luck and I chose the button, my brother would be gone. Now here is another interesting theory, but if you believe that everyone in the world came from one mother millenia ago, we're all technically "family" in that regard, and if thats the case, why the hell wouldn't you press the button, I mean, 6 billion people in the world, what are the odds you'd wind up killing the person you love?