persons. The spell allows polygamy. Also, no gender restrictions. You can marry all of your party into one big family, RAW.
You may need to check the local laws, though.
By the way, the spell does not allow for divorce - it's strictly "till death do us part".
It would generally be better to put them in pair-wise marriages, but when there's a kaiju on the loose, you can't wait multiple hours to cast it multiple times.
I once played a series of all-combat one shots, in which we could use the previous day to precast buffs. Every session we used that day to cast ceremony to make the party a polycule, until the DM banned it.
Say you have an AC of 15 and an attacker tries to hit you they roll a 15 or higher with a 20 sided dice it hits you. (Meets it beats it)
However your opponent also can have boosts to to their attack say a magic weapon adds plus 1 or something so they could roll a 14 plus the 1 to reach 15 thus hitting you. Then they roll damage with another dice dependant on the weapon.
So if the characters are then married they get a plus two to their AC and now have 17 and the 15 misses
you roll a d20 (20-sided dice) to attack someone or something. if the result is equal or higher than the AC (armor class) of whatever you hit, you succeed in hitting it
can you stack? ie, if I had a couple of clerics and a paladin, could they buff a teen coming of age, dedicate to a deity, and then marry - into some kind of broken superbuff?
yeah hard to find info on edgecases like this. if it's different ceremonies is it the same spell? sure, probably, but will try to break the dm anyway and see what happens :D