In FIFA international football or soccer, is the manager or head coach the only one allowed in coaches box or can any member of staff be in there during game?

9. THE TECHNICAL AREA
The technical area relates to matches played in stadiums with a designated sitting area for team officials, substitutes and substituted players as outlined below:

the technical area should only extend 1 m (1 yd) on either side of the designated seated area and up to a distance of 1 m (1 yd) from the touchline

markings should be used to define the area

the number of persons permitted to occupy the technical area is defined by the competition rules

the occupants of the technical area:

are identified before the start of the match in accordance with the competition rules

must behave in a responsible manner

must remain within its confines except in special circumstances, e.g. a physiotherapist/doctor entering the field of play, with the referee's permission, to assess an injured player

only one person at a time is authorized to convey tactical instructions from the technical area