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”.
No, the spell is only cast once, for all partners at the same time. “A creature can benefit from this rite again only if widowed”.
Does it stack though? If n people cast ceremony on a party, does that mean they get +2n AC?
EDIT: I read the rules. And completely read over the latter part of your comment. “A creature can benefit from this rite again only if widowed.” 😢
By the way, the spell does not allow for divorce - it’s strictly “till death do us part”.
Which has… consequences
Wouldn’t the entire policule need to be close for them to get the bonus then? That doesn’t sound like the best tactical strategy.