May 11, 2015 - 6:25 AM
I'm sorry but it's not possible to get the reservations before May 14; it's too short notice as this requires processing and shipping. It's not an online ticket. You can get the reservations locally too, but they can sell out, especially if you need them for as many as 15 people. I'd recommend to go to the rail station as soon as you arrive in Lucerne and try to purchase the reservations. If they can't sell you 15 reservations, you can still do the exact same trip, just without seat reservations and without the included lunch.
For future reference, this is the normal booking procedure: go to the last page Annika mentioned. Enter 'Luzern SGV WM Tell' to 'Bellinzona', one-way, the travel date, the Swiss Travel Pass, and 1st class. Enter 8 travelers (and later repeat this step for the remaining 7 travelers, before finally paying for all of it), this prevents being redirected to a group booking page that stops you from online booking. This will show the 11:12 AM connection from Lucerne (arrival 3:52PM), which is the one you need. I just tried and it works fine, but it can be tricky if you don't fill out the fields exactly as explained. Additionally you need upgrade tickets to 1st class but these can be purchased at the rail station in Lucerne and don't require pre-booking. Simply show your 2nd class passes and the reservations, and they will provide the upgrades.
Enjoy your stay in Lucerne!