"Are you all giving my cat milk?"
Translation:Gebt ihr meiner Katze Milch?
I realize that the Duo uses the English language phrase "you all" to indicate the plural. But it still rankles my brain every time I see it because it doesn't sound natural in English (native speaker here) and I've lived all over the States. Yes, there is a southern US expression "y'all" but that can actually be singular as well as plural. So not really the same thing.
If Duo does need a device to indicate second person plural how about "all of you?" No ambiguity there and moreover it is the title of a delightful Cole Porter song.
Y'all can go back to learning German now.