This is indeed correct, although your apostrophy is in fact an apostrophe.... I thought I would point out the correct spelling of the word seeing as this is a forum on English language. Can I suggest some additional reading: "Eats, Shoots &

The correct spelling of "grammer" is "grammar". "Nazi's", if you mean the plural of Nazi, should be "Nazis" without the apostrophe. The "s" is part of the word. "Grammar Nazis" appears to be a vocative, so I would add a comma after it. Finally,

The correct spelling would be “Smiths” as you are referring to 3 Smiths whose last name is Smith. You would only need an apostrophe if you are referring to ownership ie "The Smiths' car is red."