What is the plural of the name Frances?

It is correct to show proper names ending in -s being possessive in two ways. Most common and slightly more correct would be to add an apostrophe -s (i.e. Frances's) however it is still correct to write it as just the apostrophe without the additional -s (i.e. Frances'). To indicates multiple people named Frances, one would add the typical -es ending (i.e. Franceses).