What is the maximum number of creatures who can receive wedding rites via Ceremony?

Question

Xanathar's Guide to Everything introduces the Ceremony spell. One of the options is to perform a wedding:

Wedding: You touch adult humanoids willing to be bonded together in marriage. For the next 7 days, each target gains a +2 bonus to AC while they are within 30 feet of each other. A creature can benefit from this rite again only if widowed.

The term "together" indicates that there must be a minimum of 2 participants.

What about a maximum number of participants?

The only possible limitation I can see is the number of creatures they can fit into a 10 ft radius sphere, presumably including the caster themselves:

When you cast the spell, choose one of the following rites, the target of which must be within 10 feet of you throughout the casting.

Update: I have edited this question's title because the Ceremony spell only performs wedding rites, and the spell by itself does not constitute a legally binding marriage.

Answer 1

There is no maximum specified in the rules

You touch adult humanoids willing to be bonded together in marriage.

It doesn't say "two" or "at least two" or anything at all. The wording does imply that it must be more than one, but other than that there is nothing stated.

One thing worth noting is that the targets must all be within 10 feet of the caster so there may be a practical limit to the amount of people able to be targeted.

However, in the end, it is left up to the DM how many creatures are allowed to get married.

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On a cultural note, polygamy is actively a part of many cultures worldwide. So, while it may or may not have been the intent of the writers, the wording of the spell does indeed allow that kind of idea into the game if the DM/players want it to be.

Answer 2

What is the setting definition of marriage?

As you and Rubiksmoose noted, there is no limit on the number of creatures aside from that implied by the area of effect.

However, marriage is a ceremony or a rite, and valid participants are determined by the traditions accompanying it. If you are playing in an established setting, the DM should look at the rules and history for the race(s) of your characters to determine whether a marriage is possible.

In a homebrew campaign, the DM would either issue a fiat about marriage practices or else ask players to provide cultural background. This depends on how collaborative the game is.

The intent of the characters may be relevant as well. The effect may not apply to characters who lack the necessary passion or commitment for marriage, regardless of their participation in the rite.

Note that some cultures practice mass marriage ceremonies where many couples are married simultaneously. In this case, it may be reasonable to apply the effect to everyone involved, subject to each character being within range of its own spouse.