When to use s' or 's with names?

One Jones: "Mr. Jones's car." More than one Jones: "The Joneses' house." The rule is that you use the apostrophe at the end only when the Word ends in s because it is a plural, like Joneses. Otherwise you form the possessive with an apostrophe and an s whether or not the Word ends in s. NEVER EVER use an apostrophe to form a plural.