Remus hadn't moved away when Sirius moved closer, not wanting to make a big deal out of the questions now running through his head. 1980? Had Sirius betrayed them yet? Was he thinking about it? Would he here if he could gain from it? Was there a way to save this Sirius from making that choice? Should he? If they could get back to their proper times, would that change Remus' present by changing Sirius in the past?
As Regulus said, though, now wasn't the time to think about that. Couldn't plan for a situation they didn't fully understand.
Rolling his eyes at Sirius's look -- an instinctive gesture born of too many years spent on the receiving end of that expression, usually multiplied by James -- he turned his attention to Regulus' suggestion. "If nothing else, we probably have access to the Library. I for one would like to make sure whatever killed off the magical population wasn't some kind of curse or illness that could affect us now that we're here. And if there's no one else, we can see if the House ghosts are around, still. Nick and the Baron might be able to give us more details."