I think you might best look into the possibilities and prices of (and please note that the given prices are per person and second class)
the Swiss Card
the Regional-Pass Bernese Oberland
the Jungfrau Railways Pass
Advantage of the Swiss card is that you will save CHF 154,40 on your first and last trips from and to Zürich Airport. In between you will travel for half fare almost anywhere.
The Regional-Pass Bernese Oberland will give you 3 days of free travelling (on a 7-day pass) or 5 days of free travelling (on a 15-day pass). Two extra days of free travelling might be worth the rather small price difference between an 7-day and a 25 day pass. Advantage of this pass over the Jungfrau Railways Pass is that it covers a larger area (the Bernese Oberland instead of the Jungfrau region).
You can combine this Pass with the Swiss Transfer Ticket
which will cost CHF 127, instead of the regular CHF 154,40 on your way from and to Zürich Airport, with this ticket you will get a 20% discount on the Regional-Pass Bernese Oberland.
Information about planning trips and prices can be found here
Just want to give you some extra information about hiking tips
for the Bernese Oberland and day trips
as well. And of course the tips about hiking and safety
. Consider it an extra service from a Switzerland lover ;-)!
It is good to know that you can purchase a time table covering all kinds of transportation in the Bernese Oberland. This booklet is sold at e.g. train stations for about CHF 2.50 and sometimes it's for free.
If you choose a Swiss Card or a Swiss Transfer Ticket ordering online might be useful. The Ticket counter of the SBB railway station at Zürich Airport has limited opening hours, information can be found here
I am quite sure neither of your sons can get any reduction on the Passes I have mentioned here.
Maybe viewing this topic
may be of help too.
I hope this helps and I wish you a very pleasant stay in beautiful Switzerland!