How do I secure a mortgage on a property settlement that my ex-husband owes per our divorce. He owns an auto repair garage.

My apologies but your question is difficult to follow.  If your ex owes you money then he would sign the promissory note and mortgage.  You cannot sign a mortgage for property that is not in your name.  You should explore whether you can file a contempt in the NH case or take the NH order and seek to enforce through a Massachusetts.  In any respect, time is of the essence and you should proceed as soon as possible. Many thanks