Other contributors have said "Do you add a plural to last names?" is the same question as "What is Plural of last name?" If you believe that these are not asking the same thing and should be answered differently, click here
Simply add an 'S' at the end. For example: John and Jane Smith, would be the Smith's.However, if there is already an 'S' at the end of a name, you would put the apostrophe at the end of the 'S'. Like...