There are many sources on this. Here is one: Making Plurals of Names
If you want to make a name plural, it follows the same spelling rule as any other kind of noun.
So we write that I live next door to the Smiths.
No apostrophe--no letter is left out, the word is not possessive. We would also write that the Smiths live next to the Joneses.
is added to Jones
because the singular word ends in an s,
just like we make dresses
with an apostrophe s
just like any other noun. We could say I am Mr. Smith's neighbor.
That is the normal rule for making possessives. There is nothing different about it because it is a name. If Smith
is plural and possessive,
we would follow the same pattern that we use for any other nouns: I am the Smiths' neighbor.
Source Plurals with Apostrophes and Other Questions You Asked