I don't kow where you are moving from or how you are moving your chickens. The only reason I would even consider quarantine in your case is that your chickens might be exposed to something during the move, which they could then pass on to your brothers flock. Quarantine does nothing to show which diseases either flock has that they are immune to. It only shows diseases or parasites that the birds have picked up in the very recent past. Chickens picked up at a chicken swap are a good example of ones that may have recently been exposed. Other than recent exposure, both flocks have in effect been in quarantine for a lot longer than one month.
Different diseases are spread by different means, so different methods of isolation are required to prevent infection. Some are air born, so keeping them to where a breeze could blow dander from one flock to another would not be an effective isolation. Some are transmitted by shared drinking water or food, or direct body contact, so a wire fence between the two would provide a fair amount of protection from certain diseases, although not complete.
Complete quarantine entails completely separate facilities where there is no exchange of air, completely separate feeding and watering arrangements so you don't transmit something by the equipment, and changing or disinfecting clothing (especially shoes) when you go from one group to the other. The more of these you violate, the less effective your quarantine.
What you do is your decision and depends on your and your brother's risk tolerance. If it were me, I'd probably keep your birds isolated in the pen for a month or so, realizing that it only gives limited protection.
