This.
You add ‘s to a singular name that ends in s: Jones's
You add an es to make it plural: Joneses.
You then add an apostrophe to make the plural possessive: Joneses'
You wouldn't use Jones' as Jones is a name and although it is creeping into common usage to simply use an apostrophe, it isn't technically correct use of the apostrophe with names.
Hope that clears it up.