Apostrophe Apoplexy

We’ve gotten several holiday cards addressed to The Hirsch’s. And some of them have the senders’ name in the same form. Where in the world have folks gotten to think that the possessive apostrophe somehow can be used to denote a plural form of a name? Hey, the plural of Hirsch is Hirsches. So, if you really mean The Hirsch’s, to what of the Hirsches are you referring? And, to be even more picky, if you have addressed this implied possessive to both of us, wouldn’t it be The Hirsches’ since there are two of us?

Your’s for holiday cheer.