Hi MS, and welcome to MySwissAlps!
>> Does the Jungfrau Travel Pass cover modes of transportation in the Jungfrau region (Muerren, Grindelwald, etc.) that are not already covered by the Swiss Travel Pass?
No. Everything covered by the Jungfrau Travel Pass is also covered by the Swiss Travel Pass. The difference between them is which routes are free and which are discounted (and the size of the discount).
You can use the validity maps to see the differences:
www.myswissalps.com/ju ngfrautravelpass/valid ity
Another difference is what conditions apply to children. How old are your children?
>> We'll be two nights in Zurich and 4 nights around Jungfrau so we're trying to figure out if we need one or both passes. We are two adults and two children.
It is not usually cost-effective to get both a Swiss Travel Pass and a Jungfrau Travel Pass.
On the face of it, local public transport tickets for Zürich, point-to-point tickets to and from the Jungfrau Region and a Jungfrau Travel Pass would be a convenient choice if you are not doing day trips to other places from Zürich.
However, whether that is also the most economical choice cannot be certain without doing the sums. That means first planning your itinerary in detail, including all trips by train, bus, boat and cable car.
Then you need to look up the full-fare cost of all these planned trips and compare the total cost of separate tickets with the cost of doing the same trips with the Swiss Travel Pass, Jungfrau Travel Pass etc.
You can find fares in the Swiss Timetable.
(Use the timetable on the right with the red SBB logo)
It is important to be aware that the fare shown for any trip in the Swiss Timetable defaults to half fare, as most Swiss residents will have a Half-Fare travelcard which entitles them to this discount. Your calculations need to be based on full fares, which are double the default fare that comes up.
There is information and a spreadsheet here to help you:
www.myswissalps.com/tr ain/ticketspasses/prac tical/chooserailpass