Ghoushaubie69
I see, you’re entering the country at Tirano using the Bernina Express, where you want to reserve seats in the panoramic cars, hmmm…
No own insights into the Tirano station, sorry, as I live in a different corner of the country and have never been there. The good news is that there is a ticket office as well, open daily:
https://sbb-tickets.cc/en/travel-information/stations/find-station/station.9369.tirano.html
Anyway, 1 hour should usually be more than sufficient even for 4 people, provided there are no huge queues in front of the counter.
Otherwise there are two Plan B’s:
Consider taking a regular train to St. Moritz (R19 or RE9) instead of the Bernina Express (no seat reservations, less crowded, cheaper, flexibility to hop off/on on the way, exactly the same views).
Or bite the bullet and get the GA travelcards e.g. in St, Moritz, when you have more time.
Also you should figure out a physical address where the SwissPass cards must be sent after they have been produced (e.g. accomodation, or poste restante if possible).