I think my wife is cheating on me with 2 other men and 1 other woman?

I think they're all in on it, all against me. How else could she own both boardwalk AND park avenue within the first few turns? All of them have ridiculously huge amounts of cash, and one of them is the banker, which might explain most of the money. They keep giggling and snickering, probably while they're swapping 'Chance' cards underneath the table. I just wanted to have a nice evening of Monopoly, but they've ruined it with their cheating. My question is how can I prove they're cheating?