Here's a tip many paid and unpaid writers will find useful:
To pluralize a proper noun like "Clinton" you should simply add an "s":
ex: The Clintons are earning millions from Bill's consulting and speeches.
The proper way to form a possessive from a plural proper noun like "Clintons" is to add an apostrophe:
ex.: The Clintons' self-financing of Hillary's campaign has raised questions among progressive bloggers.
Note that you would not add an apostrophe and an "s" after a proper noun that has been pluralized:
ex.: The Clintons' income tax returns have not been released, though it is assumed that the couple files jointly. [Not "Clintons's]
