"Aren't you all Chinese?"
That is also correct, which suggests that the question is in yes-or-no format.
May I ask a question back?
In the following situations I say things this way:
(A) If I thought/assumed that all of you were Chinese, or at least some of you were Chinese, but it turned out that none of you were. I would say
(B) All of you are Chinese, and I expected something in common among you. Either you should look the same, should behave in the same way, or should be treated in the same way. It turned out to be the contrary. I would say
How would you phrase these questions in English?
I am a beginner in Chinese. I understand your question, to me the results are based on 我们都不 (you all not) and 我们不都 (you not all).
I will give you a couple solutions. You could actually make a positive statement as a question.
what Duo wants: Are all of you not Chinese
what I might say: None of you are Chinese?
B) what Duo wants: Aren't you all Chinese what I might say: Not all of you are Chinese?
That is how I interpret your questions, hope it helps.
Aren't you all Chinese?
And I believe for the second one.
Are you all not Chinese?
Im sorry I don't fully understand the question.
There must be a better way to phrase this in English because the double negative is very confusing to a lot of people.
Frustrating it does not accept 你们都不是中国人吗, I cannot tell from the English due to Duolingo's insistence on marking plural you as "you all". I suppose I will just have to memorize the answer to this question in this lesson.