In state of NJ can a stepmother be ordered to pay her husband's child support if he is no longer working?

Usually no. But unless he gets a modification from the court, he will owe the support payments. Where he gets it is up to him.

No, he should have course go back to court and get it lowered to match the new income.

But if the support is not paid, they can still arrest him, or suspend the drivers license or other things allowed in that state. So normally a family works together and helps each other out with the bills