Booking Train Tickets with Swiss Passes

Hi Vasan, and welcome to the forum. You're right, most trains within Switzerland don't require seat reservations, but international trains do. You can arrange for your seat reservations Lucerne-Milan through the Swiss timetable. Enter your connection, click 'Fare/Buy' and follow the steps in the order procedure. When asked if you have reductions for Switzerland during step 2 of the process, select 'GA' from the drop-downlist in the lower right corner for all 4 of you. This 'General Abonnement' equals the Swiss Pass in terms of discounts and free traveling. So if you select this, you won't be charged for the Swiss leg of the trip, as that's for free with the GA and Swiss Pass. Pick 1st class if you have a 1st class Swiss Pass and 2nd class if you have a 2nd class Swiss Pass.

The Swiss Pass itself can be ordered here. Just enter your country of residence and other data in the upper right corner for an overview of purchase options.