Arabs sometimes use the plural form to refer to something singular
17-1-2015 | IslamWeb
Question:
Aslama alaikum. why does the Qur'an say different things in different places? For example in one surah Allah says to Moses idhhab ills firaun. But in another surah He (swt) says to both harun and musaa idhhabaa. I'm confused one is singular implying that Allah was speaking only to musaa the other is dual. Also is surah maryam one angel tells her Allah choose her, in surah ale imran the story seems a bit different, and multiple angels tell her. Please explain it to me.
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
You should know that there is absolutely no contradiction in the Quran because it is a “masterful” (Muhkam) divine book sent down by Allaah, The All-Knowing, The All-Wise; He says (what means): {Then do they not reflect upon the Quran? If it had been from [any] other than Allaah, they would have found within it much contradiction.} [Quran 4:82] If contradiction seems to appear in the Quran, the suspect is our limited understanding.
Varied language is used in the Quran depending on the context, occasion or other specific considerations that are perceived by the well-versed scholars. The Quran was revealed in the language of the Arabs and it should be understood in accordance with their style of speech.
As for the Quranic verses about the story of Moosa (Moses) 
Al-Qurtubi 
said, commenting on the verse: {And We said, “Go both of you to the people who have denied Our signs.” Then We destroyed them with [complete] destruction.} [Quran 25:36]: “Al-Qushayri said: ‘The verse: {“Go to Pharaoh. Indeed, he has transgressed”} [Quran 20:24] does not contradict this verse [25:36] because if both (Moosa and Haaroon [Aaron]) were commanded to go to Pharaoh, then it is correct to say that each of them was commanded to do so. It can also be said that Moosa was commanded first and then when he said: {And appoint for me a minister from my family} [Quran 20:29], it was said to him: {“Go, both of you, to Pharaoh. Indeed, he has transgressed.”}[Quran 20:43]’”
Ash-Shawkaani, added: “It can be said that the fact that only Moosa was addressed on some occasions is because he was the primary messenger; and them both being addressed on other occasions is because they were both sent (to the children of Israel).” [Fat-h Al-Qadeer]
The same applies to the story of Maryam (Mary), may Allaah exalt her mention. Some verses state that angels addressed her while others state that it was one angel, Jibreel (Gabriel) . Ibn Al-Jawzi said: “A group of Tafseer scholars asserted that with relation to the verse: {And [mention] when the angels said, “O Mary,…”} [Quran 3:42], ‘the angels’ means Jibreel alone.” [Zaad Al-Maseer]
Ath-Th'alabi said: "In the verse: {So the angels called him while he was standing in prayer in the chamber}[Quran 3:39], the angels refers to Jibreel alone, similar to the verse: {And [mention] when the angels said, “O Mary…”}, which means Jibreel alone; and similar to the verse: {He sends down the angels} [Quran 16:2], referring to Jibreel alone as well. It is permissible in the Arabic language to use the plural form to refer to a singular being. For example, it may be said: so-and-so boarded the ships, while the intended meaning is that he boarded one ship. Another example is to say: he rode the delivery mules, while the intended meaning is that he rode one mule. Another is to say: I heard this from people, while the intended meaning is that he heard it from one person only. This also applies to the verse (which means): {Those to whom people (hypocrites) said….} [Quran 3:173] The verse refers to one person and not a group of people as it was revealed in relation to Nu‘aym ibn Mas‘ood 
.” [Al-Kashf wal-Bayaan]
For further benefit, please refer to Fatwa 91565.
Allaah Knows best.