Questions & Answers about Нас двое, и мы решили отделиться от группы.
Why do we use the collective numeral двое here instead of the standard number два?
When stating how many of us, you (plural), or them there are, Russian grammar requires collective numerals like двое, трое, or четверо alongside the personal pronoun. It is incorrect to say Нас два.
Why is the pronoun мы in the genitive case (нас) in the first clause?
In expressions stating the quantity of a pronoun (like there are two of us), the pronoun being counted must be in the genitive case. The collective numeral двое acts as the subject, so the structure is literally a duo of us [exists].
Why use the perfective verb отделиться after решили instead of the imperfective отделяться?
The perfective aspect is used because separating from the group is a single, completed action with a specific result that they intend to achieve, rather than a continuous or habitual process.
Is it a coincidence that both the verb отделиться and the preposition от share the same root/prefix?
No, this is a very common pattern in Russian. Verbs starting with the prefix от- (indicating movement away or separation) naturally pair with the preposition от followed by the genitive case, as seen here with от группы.