Can a creditor threaten a lawsuit when they already have a judgment?

No, send the attorney a copy of the judgment and tell him to call the Plaintiff's attorney.

No, if he does sue you then just ask for proof that he owns the debt. But he may have purchased the debt and not realized their was a judgemnt already obtained and therefore if he does own the debt he may be able to act on the judgment and try and garnish wages or bank accounts. http://www.keithdcollier.com/wage-garnishment.php If you are head oh household or file for bankruptcy protection you may be protected from garnishment. http://www.keithdcollier.com/blog/?s=head+of+household

You may have an FDCPA claim against the second attorney. He is a debt collector, and he is threatening a course of action that he cannot take - a second lawsuit.