Correct use of plural possessive rules

[Petetoni]

Peter and Toni Smith are having a party. The invite reads: Mardi Gras at the Smiths. should Smiths] be spelled with an apostrophe? Since the last name does not have an "S" is it correct to just add the "s"?

[Naz]

Hello Petetoni
Smith's hair or Smith's_______ possessive
Smiths _________ Smith family
The first refers to specific possession but the second shows his family and it does not possession.
Naz

[Gemini Alpha Female]