If two or more individuals are disfellowshipped ......for the same event........they are NOT have company with each other but are to trat each other as disfellowshipped. This rule applies to those who are simply "reproved" for an event they did together.......they are not to pal around.
This very thing happened to me and another brother for smoking pot in the 70's. We were reproved ( I was a MS at the time and lost my privledges ) He saw me one day driving and waved me over so we stopped and talked. Someone saw us because next meeting we were told not to associate with each other.
As far as I know there is no WRITTEN RULE on this particular situation.
As for sitting together in the hall........as far as 'WHAT IS WRITTEN" DISFELLOWSHIPPED PEOPLE ARE TO SIT........IN THE BACK OF THE HALL...........AND THAT'S ALL THAT IS SAID.
Gumby