two couples could split the money. I'd allow no time for conversation and no elaboration or explanation of the contest and I'd take each of the 4 people aside and ask them "yes or no, would you split the money if given the chance or not." Then, they'd only all get it if ALL 4 independently said yes.
Or here's another additional twist. Say that they do this AFTER a jury has picked a winning couple. Then you do the same thing I mention above but some extra factors. The winners are asked in private if they will share. The losing couple is asked in private "will the winning couple split the money with you". And then it breaks down as follows, although the couples are NOT told this until after they've given their instinctual answers:
1.) Winning couple agrees to share, losing couple guesses they would: everyone wins maximum prize because friendship won over greed
2.) Winning couple agrees to share, losing couple thought they wouldn't: losing couple gets nothing for underestimating their friends
3.) Winning couple doesn't want to share, losing couple thought they would: losing couple gets all of the money, winning couple loses all winnings for being greedy
4.) Winning couple doesn't want to share, losing couple thought they wouldn't: no contestant gets ANY prize. Nothing. Nada.