book Moitree Exp before arrival in Dhaka (e.g. through travel agent)?

I read that tickets for the Dhaka-Kolkata train are sold only at the Kamalapur station, and one is expected to turn up in person with passport and visa.

We are not going to be able to do this until two days before the date of the train trip (Dec 26). I know the train has not been full in the past because of the border hassle, but I also heard that things are more efficient now, plus it is vacation season. In other words, maybe there's some possibility that tickets will be gone.

Any chance that tickets can be bought through travel agents, using PDFs of passport and visa, authorization letter, etc.? (If yes, can you suggest a travel agent?) Or is there any other way to book? The bus option really would not work for us, so we'd be in a bit of a pickle if we couldn't get train tickets.

Another question: I understand that first class is sleeping berth accommodations even though it is a daytime trip. Are these berths organized as 2- and 4-berth cabins?

Many thanks,