~14 days in Switzerland

Day
1. Fly in to Zurich Airport. Train (2hr 22min) to Lausanne (5N)
2. Lausanne
3. Day to Geneva - 36min by train
4. Day to Bern - 1hr 06min by train
5. Day to Montreux - 21min by train
6. Train (2hr 35min) to Lauterbrunnen (4N)
7. Day to Murren & Schilthorn
8. Day to Wengen & Jungfraujoch
9. Spare weather day
10. Train (2hr 23min) to Luzern (4N)
11. Luzern
12. Day to Zurich - 46min by train
13. Day to Pilatus
14. Train (1hr 03min) to Zurich Airport for flight home

You could potentially use the Swiss Travel Pass for something on every day of this trip, even if only a local bus* or a museum visit. I'd spend $40 more per person to get the version for 15 consecutive days, instead of 8 days within a month. (Even leaving out days 2, 9, 11, and 14 from David's suggested plan, that still reflects 10 transportation days.)

*Local buses may also be covered by a city visit card from your hotel.

Thanks for adding that Laura. Is it not also the case that a Swiss Travel Pass will get you good discounts on mountain railways ?

Have you looked at the standard fare for each of your trips? A Swiss Half Fare Card saves you 50% discount on every travel you may take. You'll have to purchase tickets for each of your travels (at 50% reduction) and if money saving is your priority then you would do well to look into the HFC. If ease of stepping onto any train as much as you want without purchasing tix for every journey - then the STP is a better choice...but maybe not as much cost savings.