I wouldn't have thought it made much of a difference to the steward. When I've travelled with family previously they have checked in with the steward meanwhile I'm off photographing the engine so the only time I've seen the steward would have been in the morning when breakfast was delivered, a touch too late to say much if anything I guess?
If you are really worried talk to the steward and explain the situation, they are human and are meant to be there to give good customer service. If you don't feel confident doing that then you could always wait until the last minute in the Paddington First Class lounge so there is little time to say anything about it? The cabin is quite small so you might be grateful for the more spacious surroundings, free drinks and snacks in the lounge?
I guess it depends on the cabin you have too, is it the twin as in two cabins with the connecting door opened between them or two berths in the one cabin? If the former you could always suggest the connecting door is locked and the cabin sold to on the night passengers by way of compromise?
Enjoy the Volo TV experience and have a wonderful trip, do wave as you pass Reading. You may find the doors aren't unlocked at Reading BTW, when I did it from there the train manager was getting everyone to board from a door near the buffet, I guess this preserves the overnight security to some extent ensuring only ticket holders board, sadly my cabin was pretty much the last one (certainly the very back carriage) so on realising this he released the doors so I could board without having to go through the narrow corridor.
In a similar vain to your question I've often wondered when looking at the cheap prices for the Caledonian Sleepers about doing something similar myself and booking two bargain berth tickets to give myself a private cabin at a good deal less than the cost of a solo supplement and ticket, has anyone got experience of doing this?
