(All prices here concerning tickets/passes are given single, second class and per person.)
"Rail Pass" is a generally used term, suggesting that these Passes are for trains, but they are also for boats, buses, mountain railways, cable cars, gondolas etc.
During your two weeks stay you will probably use other kinds of transportation than only trains! But as you don't mention these, it is a bit difficult to give you good advice.
First, the regular prices for the trips you mention, using the Timetable Switzerland
- Zürich City transport - free with some Passes
- Zürich - Grindelwald CHF 77,20
- Grindelwald - Interlaken CHF 10,20
- Boattrip from Interlaken on Lake of Thun CHF 65,00 (price roundtrip), or
- Boattrip from Interlaken on Lake of Brienz CHF 46,00 (price roundtrip)
- Grindelwald - Lauterbrunnen CHF 8,20
- Lauterbrunnen - Kandersteg CHF 31,00
- Kandersteg - Chamonix CHF 40,00 (depending on day course)
- Chamonix - Geneva French ticket
Adding up what I have so far, total will be a little less than CHF 250
If one travels rather extensively by train, it is usually good to consider a Swiss (Saver) Pass.
A Swiss Saver Pass
(15% discount when travelling together) for 15 days will cost CHF 387,00 (per person).
Please check the area of validity of the Swiss (Saver) Pass
. Here you can see where you can travel for free en where you can travel with discount. Note that this Pass will bevalid between Martigny and Chamonix, although a 50% discount cannot be garanteed.
As I said, I guess you will be using forms of transportation (other than just the train trips you indicated) in a way that could make this Pass a right choice.
A Swiss (Saver) Pass is certainly the most convenient of all Passes as you "almost never" have to buy tickets: just go on a train, bus or boat, your Pass is your ticket.
Just to be complete please view the possibilities and prices of the Swiss Half FareCard
as well. This Card has a validity of one month and will cost CHF 99 per person.
It will give you a 50% discount on travelling by train, bus and boat and also 50% discount on many gondolas, funiculars and mountain trains. Please check the area of validity of the Swiss Half Fare Card.
I hope this gets you started and I wish you both a very pleasant stay in Switzerland!