Questions & Answers about ¿Vosotros dormís aquí de noche?
Wait, I thought dormir is an o-to-ue stem-changing verb. Why is it dormís and not "duermís"?
That is a great catch! You are right that dormir is an o-to-ue stem-changing verb (for example, yo duermo). However, in the present tense, the nosotros (we) and vosotros (you all, used in Spain) forms never get the stem change. Because of this rule, the original o is kept in vosotros dormís.
Why does dormís have an accent mark on the letter i?
In the present tense, the vosotros ending for all regular -ir verbs is an accented -ís (like vivís or escribís). This accent mark tells you to put the speaking stress on that final syllable.
Why does the sentence use de noche instead of translating the English word "at"?
Languages often use different prepositions for expressions of time. In Spanish, de noche is a very common set phrase meaning "at night" or "nighttime." You will also frequently hear por la noche, which means the exact same thing.
Is the word vosotros strictly necessary here?
No, you can safely leave it out and just ask ¿Dormís aquí de noche? Because the verb ending -ís is only ever used for vosotros, the listener already knows exactly who you are talking to. Including the pronoun just adds a bit of emphasis.