Translation:Voi ați mers împreună cu fratele ei la magazin?
Why does "Ati mers cu fratele ei la magazinul" not work?
The usage of the definite article is different in Romanian, compared to English. See this thread for more info. In this case, you must not use an article for "magazin", so the correct version would be:
Wow. potestasity put in some work on that response. Thanks for leading me there!