Controversial: Writing With (AP) Style

On first reference, you use a first and last name: John Smith. But what do you do on a second and subsequent references?

Here is AP Style, under names:

In general, use only last names on second reference.

But what if there is more than one person with the same last name? AP Style has that covered, too. Also under names:

When it is necessary to distinguish between two people who use the same last name, as in married couples or brothers and sisters, use the first and last name.