Depends which route, there are 2, the lowland sleeper which travels between London and Edinburgh/Glasgow(splitting at Carstairs) and the Highland Sleeper which travels between London and Inverness/Aberdeen/Fort William splitting at Edinburgh Yard - no passenger are able to disembark here but it does pick up an extra coach and baggage for the Fort William Portion. Class 67's only operate north of Edinburgh unless the London trains are diverted off the wires
So in effect you have 7 different consists, the shortest being the FW portion which in winter can be just 1 Sleeper, 1 Coach and 1 Café & 1 Baggage(sometimes not even the baggage) and the longest being the Full Highland Sleeper from London which is 2 Coaches, 2 Baggages and numerous Sleepers double headed by Class 90's or Class 92's
FWIW The Caledonia sleeper are phasing out and will no longer uses Class 67's north of Edinburgh since it was taken over by serco as they are now using Class 73's which where built in the 60's as they are more suitable for the routes (especially the FW route)