Its "Tom Smiths". Think of it this way: You are not saying there are many Toms, you are saying there are many of them with the same surname, "Smith". In the same way, we don't say, "There are Trump's Tower all over the world", we say, "There are Trump Towers all over the world". It's no different if the first word of a two-word proper noun includes an apostrophe, such as Bob's Bakery. In this instance, we would say, "There are two Bob's Bakeries in the city."
In short, the second word of two-word proper noun is made plural when we are talking about more than one of that proper noun.
examples:
- We own two Apple Macbooks; not Apples Macbook
- There are not two White Houses in the US; not Whites House.
- There are many "Tom Smiths" in the Manhattan phone book; not "Toms Smith".
