"Did you reside together?"
Translation:Bodde dere sammen?
If you were asking two people if they lived together clearly this sentence would be used, but what if you were talking to one person and asking if (s)he and another person (who is not present in the conversation) lived together? Would you use du because you're talking to one person, or dere because you're talking about two people? I assume dere?
You would use 'dere', or you could rephrase the sentence: "Bodde du sammen med ham?" = "Did you reside together with him?". "Bodde du sammen?" would not work.