Let's Clear the Air on a Common Grammar Mistake

My dear friends Anthony and Trina Morella of Las Vegas called me this morning to settle a grammar argument.
The two of them, along with their adorable son Zachary, went to have family portraits taken.
At the bottom of one of the photos, the photographer put, "The Morella's."
Trina, after my own heart, refused to hang the photo in the house because it's not grammatically correct to write, "The Morella's."
Trina is absolutely correct. Under no grammar rule is it correct to make possessive "Morella" in that case.
Anthony says to me, "So why do we see family names written like that all the time?"
I said, "Just because society embraces it does not make it correct."
To get around this, I recommend adding an "s" to make it "Morellas" or writing, "The Morella Family."

Here's the explanation for it, from a grammar web site I sometimes use:

When a family name (a proper noun) is pluralized, we almost always simply add an "s." So we go to visit the Smiths, the Kennedys, the Grays, etc.When a family name ends in s, x, ch, sh, or z, however, we form the plural by added -es, as in the Marches, the Joneses, the Maddoxes, the Bushes, the Rodriguezes. Do not form a family name plural by using an apostrophe; that device is reserved for creating possessive forms.