The Smiths are a family; you make the word Smith plural by adding an s, not with an apostrophe and an s as you would for that smith’s workshop. Whether the plural noun Smiths then needs to be made possessive is a different matter altogether, since both a friend of Jim and a friend of Jim’s exist. It thus follows that friend of the Smiths and friend of the Smiths’ can also both peacefully coëxist. Certainly your ear cannot tell them apart, only your eye. See the linked answer for more.
– tchristFeb 02 '19 at 04:46