Help me choose one of these:
Sigmund, the doorman – and his counterpart, Siegfried, the night watchman – were responsible for ensuring that every person entering and leaving the building signed the daily log.
or
Sigmund, the doorman – and his counterpart, Siegfried, the night watchman – was responsible for ensuring that every person entering and leaving the building signed the daily log.
or
Sigmund, the doorman, and his counterpart -- Siegfried, the night watchman -- was responsible for ensuring...
or
Sigmund, the doorman, and his counterpart -- Siegfried, the night watchman -- were responsible for ensuring...
or maybe with commas instead of the dashes.
Sigmund, the doorman – and his counterpart, Siegfried, the night watchman – were responsible for ensuring that every person entering and leaving the building signed the daily log.
or
Sigmund, the doorman – and his counterpart, Siegfried, the night watchman – was responsible for ensuring that every person entering and leaving the building signed the daily log.
or
Sigmund, the doorman, and his counterpart -- Siegfried, the night watchman -- was responsible for ensuring...
or
Sigmund, the doorman, and his counterpart -- Siegfried, the night watchman -- were responsible for ensuring...
or maybe with commas instead of the dashes.