Definitely worth investigating because Swiss rail (especially the mountain bits) can be EXTREMELY pricey.

I suggest that you start with googling Swiss Rail, Schweitzebahn, CFF/SBB etc on a search engine and then follow it up with FAMILY RAIL CARD. You will be able to get the details in German, and possibly also English. If boats are involved, such as with the round trip of Mount Pilatus starting and ending in Luzern, it still reduces the total. If you want to do this, might I suggest that you take the cable car UP (via Horw and Kriens) and come back on the rack railway (much more exciting views of the gradient) and take the boat connection back to Luzern rather than the train (unless you have little time). You can leave your car in the station garage, as the trip starts with the bus opposite the station to Kriens, and ends back at the station or at the boat landing stage directly opposite the station.

Expect to feel lightheaded (not JUST because of the enormous cost) if you go up the Jungfrau (definitely worth it, even if the weather isn't clear). The rail pass will give you reductions up the Piz Gloria, but ALL CATERING on the mountain tops is VERY COSTLY!!!

Have a great time! I wish I was coming too!

Thanks for that really useful information - I'm off to do some research on those suggestions.