If there is going to be a probate, you need to get Domiciliary Letters from the Court after you start a probate case.
However, if everything was owned together with your husband, and there will be no probate, then you can use a Circuit Court Form PR-1831 (link to download page below). The form can be completely and properly filled out, and signed by you, then you can take care of these types of things.
I am not your lawyer. Any advice given through the Avvo site is for hypothetical purposes only, and does not create an attorney-client relationship. The advice is without warranty and you should not rely on this advice without consulting a Wisconsin attorney directly who knows the particulars of your case.
I agree with Attorney Krause's answer to your question and just wanted to add a few practical tips. The The Wisconsin Circuit Court Form PR-1831 (Transfer-by-Affidavit) can only be used if the the checks you are seeking to have reissued in your name are worth less than $50,000. Your signature on the form must be notarized. Finally, send the original checks back to the mortgage company with the completed and signed Transfer-by-Affidavit and ask if they want a death certificate as well. Best of luck and sorry for your loss.