In the age of airbrakes and union contracts you would have a 5 man crew. The conductor and senior brakeman would be in the caboose, the engineer fireman and junior brakeman would be on the head end.
The headend man would wind up doing most of the work over the road, and have the less comfortable seat. Hence why he would have the lowest seniority.
Yard crews could have more crew members assigned, especially if hand signals needed to be relayed
We lost the fireman in the 1960s to 70s.
Lost the rear brakeman in the late 70s to 80s
Lost the headend brakeman in the 90s
Now the conductor is the next one in the crosshairs, will see what the future brings.
As far as the early days before airbrakes, you weren't likely to see a hundred car train. With some notable exceptions, 25 to 40 cars and about 1000 to 1500 tons was considered to be the limit of safety at the time. A train would have 2 to 5 brakeman depending on length, grades territory.
Train crews would rest in the caboose, engine crews would stay at a bunkhouse at the away terminal.