if its a family you know, you can just print their last names as familia Smith Jones. In Spain we use the two last names one father one mother ::) given credit to the Mom!
if its one person, you can write the name John Smith Jones y familia. No need to put Mr or Mrs unless you hardly know them but for Christmas card, then you know them ::)
You can say Feliz Navidad y Prospero Anho Nuevo (need to use the N word in Spanish my keyboard wont let me)