That's not going to stand up in court.

Expect them to deny everything and expect him to have retained another address - even if it's on paper.

But more to the point...unless they're married (and even then at times), he can still be required to pay child support even if they're all living together.

What you can do is file in court for contempt for non-payment. Leave the rest alone because in all honesty even if you report him and their benefits stop...do you seriously think that you're going to start getting regular payments again based on that?

THEIR income will decrease significantly and you'll probably have even less chance of collecting.