Mr. Jones has an ornmanent.
Mr. Jones' ornament looks nice. (possessive option #1)
Mr. Jones's ornament looks nice. (possessive option #2)
The Joneses, meaning Mr. and Mrs. Jones, have an ornament.
The Joneses' ornament looks nice. (possessive option #1)
The Joneses's ornament looks nice. (possessive option #2)
Mr. Smith has an ornament.
Mr. Smith's ornament looks nice. (possessive)
The Smiths, meaning Mr. and Mrs. Smith, have an ornament.
The Smiths' ornament looks nice. (possessive options #1)
The Smiths's ornament looks nice. (possessive option #2)