I am looking for a divorce lawyer for my son in law that will take payments after a settlement has been agreed upon

While I can't speak for every divorce attorney, most attorney's will want a retainer (advanced fee) up front before taking the case and most bill at their hourly rate. What you are proposing poses a big risk for the lawyer that either they don't get paid at all or the settlement isn't sufficient to cover the fees involved. Attorneys also in Wisconsin  cannot use a contingency contract for payment of fees in a divorce.