- No , it means, that the reservation is included in the ticket, if you buy one normal ticket that is. It also means a reservation is mandatory on that train, unfortunately this particular night train can only be booked at the station in Hungary.
- Generally speaking domestic seat reservations are not bookable outside of Romania, so you would need to go to the ticket counter at Brasov station. But your second train should be rather cheap (as rail transport is in Eastern Europe) so if you have a flexipass (i.e. x days in y months) It would be a waste of travel days to use it on such a journey. Better buy a full fare ticket on the cfr calatori website (and tickets can be purchased online).
Your first train continues to Bucarest anyway, is there a reason for you to change at Brasov ?