Weirdly, due a certain notion of etiquette, English grammar requires that the first person pronoun ("I" or "we") must follow the third and/or second persons in this kind of construction, unless something that is a matter of shame. "Pete and I created this masterpiece." "Pete and I had coffee." "Pete and I are night owls." BUT: "I and Peter committed this crime, your honor."
Romanian insists that we put the first person pronoun first. The difference at hand is the point here.
That is interesting, I was not aware of the word order changing depending on shame.
It seems to me that most people in the UK these days would say “Me and Peter committed the crime” which I think is wrong but I seem to be in a minority. The funny thing is “I and Peter” sounds wrong so I would say “Peter and I”. I think the people who say “Me and peter” would be happy with “Duo and us” rather than “Duo and we”. It is a matter of whether the phrase is the subject or object of the sentence.
Returning to the original sentence, consider this: “Us are night owls” sounds very wrong, everyone would say “We are night owls". Including the words “and Duo” in the sentence should not change the “we” into “us”. So I would say that you are correct to say we should use “we”.
Sorry to be so pedantic!
This doesn't always work, but a good rule of thumb for saying "I" or "me" in a sentence is to take out the other subject of the sentence. For example, take the phrase "He and [I/me] went to the store." If you take out the third-person pronoun, you make the sentence either "I went to the store" or "Me went to the store," so here you would say "He and I went to the store." In the sentence "What about him and [I/me]?" you can do the same thing: "What about me?" works, and "What about I?" doesn't.
Of course, this doesn't really matter in colloquial language. Plenty of people say "Me and him did this," for instance. I think it's because it's considered more polite to put someone else in the sentence first, listing subjects or objects in such a way that you (the first-person pronoun) comes last.
It absolutely is. It's not often used and it sounds weird, but in formal English you always use subject pronouns in the subject of the sentence. We are night owls. We (and Duo) are night owls.
That said, if you don't want to sound like a robot, in colloquial English you'd use "Duo and us" or just rephrase the sentence altogether. "We and Duo" is awkward English, but it is correct English.