What is the official word that refers to both bride and groom?

'The espoused' refers to both persons who are engaged to be married.

Oxford English Dictionary :

espouse

1946 O. F. Grazebrook Nicanor of Athens xi. 159 Take your pleasure now, but know that I have espoused you to Chrysilla..and you will marry her.

(a) transitive. To give in marriage; to marry (a person to another, esp. a woman to a man; formerly also with †with); to arrange for (a person, esp. a woman, or a couple) to be married; to betroth.

(My additional note : Using the past participle with an article "the espoused" denotes those who are engaged and are pursuing the activity of espousal.)

Betrothal (also called espousal) is a formal state of engagement to be married.

Wikipedia - Engagement

If they're married, you could call them newlyweds.

Newlywed (noun): Someone who has recently married.

Example: The hotel has a special discount rate for newlyweds. [Cambridge English dictionary]

If they're not married yet, you could use affianced.

Affianced (adj): [literary] Engaged to be married.

Example: An affianced couple. [Lexico]

There is no single word that is really commonly used. Some might be accurate, but they are so uncommon as to sound strange to some people.

I would say the most accessible single word is betrothed:

[Merriam-Webster]
adjective
: engaged to be married a betrothed couple
// … clasped hands, signifying the bond between betrothed men and women …
— Mary Feilden
// For three years she and Emilio Estevez were an item and were even betrothed for a time.
— People Weekly

noun
: the person to whom someone is engaged to be married
// … she put on her grey silk gown and her cherry coloured ribbon with as much care as if she had been herself the betrothed.
— George Eliot

Used as a noun, the betrothed can refer to a single such person, a couple, or multiple people.

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In terms of commonality, Google Books Ngram Viewer shows that the betrothed is more common than the espoused, the affianced, or the postulants (and note that espouse also has the second sense of supporting a cause, meaning its engaged sense is even less common):

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Although the betrothed is arguably the most common and least esoteric of possible phrases with an article and a noun, I'd say it can't be as natural as just using the bride and groom in the first place (or the brides or the grooms in the case of same-sex marriages), or something like the happy couple where the context is known:

You can say "the bridal couple."

Ex. The bridal couple and their attendants all wear yellow ribbons today in remembrance of the groom's father.