Who has the guns now? Another member of the family? If you don't especially want the guns, you can send a notarized letter to whomever, in MI, has the guns, authorizing him/her to sell the guns on your behalf and send you the money. A quick sale to a dealer won't get full value, but will get rid of a headache.
Alternatively, contact a CA dealer and ask him to send a copy of his FFL to the person who has the guns. With that, they can ship the guns to that dealer by UPS or have an MI dealer ship USPS (this is usually cheaper than UPS but the shipping dealer will charge a fee). In any case the receiving dealer will charge a fee for the paperwork in CA. AFAIK not even CA bans such old guns, but the whole CA system was invented by insane legislators and is enforced by even more insane police, all scared to death of those awful Mexicans gettng guns.
Jim