Presidents Elect or President-Elects?
Solution 1:
Presidents-elect. Pluralize the noun.
cf. Words that are pluralized in the middle?
see AP Stylebook:
- Significant word first: adjutants general, aides-de-camp, attorneys general, courts-martial, daughters-in-law, passers-by, postmasters general, presidents-elect, secretaries-general, sergeants major.
- Significant word in the middle: assistant attorneys general, deputy chiefs of staff.
- Significant word last: assistant attorneys, assistant corporation counsels, deputy sheriffs, lieutenant colonels, major generals.
Addendum:
Language obviously changes over time. At the moment, traditionalists like AP Style prefer to pluralize president-elect as presidents-elect. Other arbiters of acceptable usage, e.g. Merriam-Webster Learner's Dictionary and reputable organizations like CBS News, ABC News and Pew Research Center consider president-elects the proper pluralization.
The U.S. Senate's website devoted to the presidential inaugural ceremonies pluralizes both ways on the same web page. This gives a very clear example that usage is in flux. See the two examples below. The differing pluralizations follow directly one after the other without any intervening text.
The following list provides information on Inauguration Day worship services attended by Presidents and Presidents-elect since 1933.
WORSHIP SERVICES ATTENDED BY PRESIDENT-ELECTS
Solution 2:
Preferably, the same way you would write the singular noun (which can vary according to style), but with the head noun pluralized. So if you write President-elect, the plural is Presidents-elect; if you write President elect then Presidents elect.
For whatever it matters, the Presidential Transition Act of 1963 uses the terms "President-elect", "Vice President-elect", "Presidents-elect", and "Vice Presidents-elect". The 20th Amendment, on the other hand, uses the terms "President elect" and "Vice President elect" and makes no use of the plurals.
"President-elects" is valid in the sense that you can tack an -s onto any English noun and generally be understood, but it has a great deal of tradition working against it. "President elects", without the hyphen, also has the disadvantage of being confusable with President (singular noun) elects (verb).