Author(s) last name(s) (to use possesive or not)

Dispense with the use of apostrophes and parentheses altogether by changing the way the possessive is expressed:

the names of one or more authors

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In cases like this, where trying to come up with the correct way of writing something always produces something that looks wrong, you need to rephrase it.

Even if there is only a single author, the plural is allowed when using one or more.

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There are variations to this that retain the apostrophe:

any author's last name
the authors' last names

The second might be possible, given the context of the phrase, but the first should always be correct.

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Also, again depending on the context of the phrase, the following simple replacement is possible:

last names