Plural does NOT have an apostrophe - you never make words plural by adding an apostrophe unless you are talking about words like CD or DVD - then it is acceptable, but not necessary.

To make words plural, you add an "s" or "es" and the same is true for names. The Valdezes, the Smiths, The Williamses, etc.

You add an apostrophe to show possession, not plural.
I am an English teacher, so you can trust me. ;)