Odd. S-apostrophe is generally only reserved for plurals. Words like “walrus” and “altas” and the such should all get the apostrophe-s, at least according to every style manual I’ve ever seen. “Waitress,” “strewardess,” and the such usually get apostrophe-s, but I do know of one, frankly bizarre, exception. AP Style treats those as getting the apostrophe-s, unless the next word begins with “s.” Therefore, “waitress’s uniform,” but “waitress’ smile.” The latter looks all kinds of wrong to me, but there it is.
The example you give is wrong – it’s keeping up with the Joneses, plural, not Jones’s, possessive, or Joneses’, plural possessive. It may just be a poor choice of example, since we’re talking about possessives, not plural.
Apostrophe-s is never used to indicate the plural (except in very rare and odd cases such as the plurals of letters (p’s and q’s)).
Oh, and lest there be any confusion, I mean the possessive of plurals.
When in England, I always have a couple pints of Banks Ale, but the barmaid always gives me “Banks’s” (Bankses).
The Chicago Manual agrees with this one. It’s the same rule everyone else is mentioning: if you say /-ez/ or /-es/, you should write the s. If you don’t, you don’t. When there are a couple of -s- sounds in a row (the waitresszsmile) and the sounds run together and you don’t really say the 's as an extra sound, therefore you don’t write it.
Of course, in my head, it’s wait-ress-iz-smile, and the example looks / sounds wrong to me, too, but it’s hard to second-guess your own speech patterns.
I’d be really surprised if there’s a lot of people who don’t pronounce the possessive-s in “waitress’s smile.” I assumed the AP rule was just some quirk that four esses in a row look funky. The only instance I could think of where I don’t pronounce the possessive-s is in fixed expressions like “goodness’ sake”
Apparently, according to this, there are style guides that don’t even like three esses in a row:
Actually, Chicago specifically excepts Biblical and ancient names ending in S (Jesus’, Xerxes’) and a few others (ends in a silent “s”: Camus’).
To answer the OP’s question, though, I’ll admit that when I’m speaking, rather than writing, I’ll say “Jesuses [followers].”
You mean “Keeping up with the Joneses.” That phrase means “keeping up with the people named Jones,” making Jones a plural, so it would be “Joneses.”
The POSSESSIVE of Jones is Jones’s; “That is Mr. Jones’s car.”
As my last name is Jones, this is important to me. 
Keeping up with the Joneses’s possession-saturated lifestyles?
No, in that case, single apostrophe: “Keeping up with the Joneses’ possession-saturated lifestyles.” Joneses is plural, and plural possessives get the single apostrophe.
Drat!