"You all are going to Great Britain."
Translation:Ihr geht nach Großbritannien.
I think that's right. "you all" seems to be a typical mark of sentences from the Pearson course ( https://www.duolingo.com/comment/24052907/Duolingo%E2%80%99s-Partnership-with-Pearson ) when they want you to answer with ihr.
It's not a usage that's typical for the public course created by community volunteers and causes confusion due to the inconsistency.