angels in Surah Al Imran

 From the book “Al-Mufassal fi al-Radd ‘ala al-Shubuhat A’da’im al-Islam” - Ali bin Nayef al-Shahood:

How many kings preached it? In Surah Al Imran: “When the angels said, ‘O Mary, indeed Allah gives you good tidings of a word from Him, whose name will be the Messiah, Jesus, the son of Mary - distinguished in this world and the Hereafter and among those brought near (to Allah)’ (45).” Here there is more than one angel, while in Surah Maryam, only one angel gave her good tidings and said to him: “She said, ‘How can I have a boy while no man has touched me and I am not unchaste?’ (20).”

The answer: The majority of commentators agree that what is meant by the angels in the Almighty’s statement: “When the angels said, ‘O Mary, indeed Allah gives you good tidings of a word from Him, whose name will be the Messiah, Jesus, the son of Mary - distinguished in this world and the Hereafter and among those brought near (to Allah)’ (45).” Mary, indeed Allah gives you good tidings of a word from Him…” That He alone is our master Gabriel, peace be upon him.
The Arabs sometimes use the plural form to describe a singular person because they mean the genus. [1]
Like when you say: “I rode cars from Damascus to Amman” (and you only rode one car).
And when you say: “I saw the messenger traveling by postal bicycles” (and he only rode one bicycle).
And from this is the saying of Allah the Almighty in Surat Al Imran: “Those to whom the people said, ‘Indeed, the people have gathered against you, so fear them…’” [Al Imran: 173]. And the speaker is one. [2]
And it does not prevent a group of angels from giving her good tidings after our master Gabriel gave her good tidings… in a different gathering.
That is, our master Gabriel gave her the good news at the beginning.. and after a short period of time, other angels came and gave her the good news.
Repeating the good news is necessary to confirm and honor it, and to emphasize the importance of the matter, and to establish certainty in the truth of the good news and that it is not an illusion or a dream, and in repeating the good news also: giving her the good news of things in addition to what she was given the good news of in the first good news.


Footnotes:
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[1] Abu Ali Al-Marzouqi said in his book Al-Amali, p. 104, after explaining the eloquence of that: “Don’t you see that it is appropriate to say to someone who owns a slave, or gives a dinar: You have come to own slaves and give dinars, even if he only owned or gave a dinar?”
[2] The speaker: Nu’aym bin Mas’ud, and it was said someone else, and what is meant by the people who gathered for them: Abu Sufyan. See: Mufhamat Al-Aqran fi Mubahmat Al-Quran, Al-Suyuti, p. 12.

http://islamport.com/w/aqd/Web/3906/1844.htm

(42) “And when the angels said, ‘O Mary, indeed Allah has chosen you and purified you and chosen you above the women of the worlds.’” (42)

“And when the angels said,” meaning Gabriel, peace be upon him, and the reason why the Truth mentions this with “the angels said” is because the speech of the speaker - meaning the human being - has - as we said - an angle of departure from which the sound comes.

You can be sure of this when a sound comes to you, as you find your ear inclining toward the source of the sound. If the sound comes from your right ear, you turn and lean to your right, and if the sound comes from your left, you turn to the left. But the speaker here is Gabriel, peace be upon him, and his voice comes from every direction, so the matter becomes strange, which is why the speech was attributed to the angels.

Source: Interpretation of the Holy Quran by Sheikh Muhammad Metwally Al-Shaarawy

The general rule: The Arabic language alternates between plural, dual and singular.
It often uses the plural for singular and dual, and uses the singular for plural and dual.
All of these are linguistically correct aspects, there is nothing wrong with that.
The examples from the Qur’an, the authentic hadiths of the Prophet, and the poetry of the Arabs are countless.

As for the case in question here: The most acceptable and logical opinion (as our brothers mentioned) is that Gabriel, peace be upon him, informed her at first, then the good news followed.