They only have one crew anyway, they travel between sites.
How do the shunting crew travel from Carstairs to Edinburgh and back? Does the loco that takes the Edinburgh portions to and from Carstairs run light engine back to Edinburgh in between, and if so do the shunting crew ride with it?
Actually (more complicated question) how many class 92s are actually used every night? As far as I can see, it could be done with six,
1. ECS Highlander stock Wembley to Euston, then Lowlander Euston to Glasgow
2. Lowlander Glasgow to Euston, then ECS Highlander stock Euston to Wembley
3. ECS Polmadie to Edinburgh, Edinburgh to Carstairs, light to Edinburgh, Highlander Edinburgh to Euston
4. Highlander Euston to Edinburgh, light to Carstairs, Carstairs to Edinburgh, ECS Edinburgh to Polmadie
5. ECS Polmadie to Glasgow, and back in the morning
6. ECS Lowlander stock Wembley to Euston, and back in the morning
but I'm fairly sure there are more - for example in my experience both Highlander and Lowlander ECS runs to/from Wembley have a loco on each end, rather than using the loco from the first arrival, after release from the stops, to take the second departure. Also, if one loco works both Edinburgh Carstairs and return, that has to be additional to the two working the Highlander.