Reported - this should be 'there are eight of us (in total)' I think. 'We are eight' seems like a literal translation but you wouldn't hear a native speaker say it.
I too said "There are eight of us in total" and agree that it is a much more natural way to say it.
I agree with you both, although this would also be acceptable.
It's not true that natives wouldn't say this. I've heard it said, and I've said it. It is, however, a bit formal.
Why isn't "There are eight of us in all" correct? It marked me wrong because of the phrase "in all" as opposed to "in total."
I put "There are 8 of us." that makes waaaaaaay more sense.
A better English translation could be There are eight of us altogether. The translation given would not be said in the USA.
I tried: we are eight altogether. It was accepted.