Metroliners on N.E.Corridor trains usually ran in 4or 6 car trains. Usually they would have at least one Snack Bar Coach on each train, but I don’t recall about the Parlor Cars. They didn’t have to run in multiples of two and sometimes would run in three car trains (rarely on the N.E.Corridor, but quite often on the Harrisburg trains)
The cab (front) end of the cars had retractable diaphrams and passengers could and did walk through the entire train.
The pantograph (rear) end of the cars had fold-down steps for use at low-level platforms.
Hi - all the “Metroliner” EMUs had couplers at both ends, so they could be made up in pairs of back-to-back cars in any arrangement you wanted. As noted the most common arrangements were as four- or six-car trains. For a while there was a non-stop round trip which ran through Phila via the “high line”, so passing up 30th Street Station altogether. Although the trains could run as an 8-car train, I don’t know that the traffic demanded this. So multiple coaches in consist with one cafe car and one parlor car is the way the trains were made up. As built, the parlors had 1-1 swivel seats until later rebuilt. In answer to the question about walking from car-to-car, yes this could be done. Greatest part of these cars was that you could ride up front with the engineman and look over his shoulder, out the glazed part of the front train door, etc. I know these cars challenged the maintenance forces, but I did have some great rides on them. Hope this is of some help, Art