Thanks for the all the replies.
I guess I worry too much about the domino effect. What if she did go to jail? What if they had to repay all that money - it is probably getting close to $100000? What if their 2 children suffered? I would feel so much guilt and I would also worry that they would find out it was me because they can be nasty people sometimes.
I actually can't believe they haven't been dobbed in yet because its not exactly a secret. I don't want to see them punished I just want them to stop cheating.