grammatical number - When to use an apostrophe when your last name ends with an s

Shortly after my wedding day my wonderful mother-in-law sat me down to say that my new name Barnes was to be spelled (in Christmas Cards) Love from the Barnes'. She went on to explain that her German mother-in-law had the same talk with her regarding Christmas Cards. So, in keeping with family tradition I have always said with love from the Barnes'

Now they are both on the other side and I am gaining a wonderful daughter-in-law and plan to keep the tradition going. But I am curious if it's grammatically incorrect.

Thoughts??