the answer is ...it depends, but here are some numbers:
The 12-1 includes 12 open sections and 1 drawing room. A section includes an upper and lower berth, but except during high demand periods, passengers could pay a small up charge and get the entire section to themselves. The lower berth could sleep 2 (close friends) and 1 in the upper berth, so up to 3 per section. The drawing room had 3 berths, so the maximum number of passengers could be 39, but this would be very unlikely, since many passengers traveled solo. With all solo passengers, the maximum would be 27 if all all section berths and the three drawing room berths were occupied (unlikely). The drawing rooms were also used by families, so sometimes kids would share berths, further complicating the numbers.
Same story for the 10-1-2: 10 sections (10 x 2 berths, up to 3 passengers), 1 drawing room (3 berths/passengers), and 2 compartments (2 x 2 berths/passengers). With one person in each berth, there would also be 27 passengers.
Then, as now, passengers paid separately for rail travel (fare to the railroad), and accommodation charge (sleeper accommodation or parlor seat to the Pullman Co.).
