When do you use an apostrophe S vs. not.
Lordy Lordy Lontin's are forty or
Lordy lordy Longtins' are forty
Lordy, Lordy, Lontins are forty.
If the family name is Lontin and there's more than one of them, then add -s, like this, Lontins. As for when to use apostrophe s:
Ex: This is John Lontin's dog. <just one Lontin>
Ex: This is the Lontins' dog. <more than one Lontin>
Does that help?