Rail Pass Advice

Last question first. 2nd class is perfectly comfortable on Swiss trains. You will not be riding them for that long, so I see no reason to spend extra for 1st. There is no 1st class on the Schilthornbahn, or the Stechelberg bus, so even if you did spend the money, often there is no 1st class available.

With 4 nights in Gimmelwald, you only need a pass for 5 days, and like you say, there is no 5-day B.O. Pass. So no reason to spend extra for a 6-day when you cannot use one of the days. Surprisingly, your lowest cost option is to buy the Half Fare Cards and the 3-day B.O. Pass for the 3 full days you are there, and just use the Half Fare Cards for your arrival and departure days.

One other way to save a bit of money is to buy Saver Day Passes soon for your arrival and departure days. With the Half Fare Card, it costs 29 CHF when bought way in advance. That is a bit less than the Half Fare prices for Basel to Gimmelwald and Gimmelwald to Zurich. You know the days, so you can buy with confidence.

On Paris - Switzerland I would book 1st class on the TGV if you can get a good price (which is often the case). What you can do is book Paris - Gimmelwald on www.sbb.ch in advance, and you will get a discount on the Basel - Gimmelwald part. Combine that with a 4 day Berner Oberland pass, and a Supsersaver ticket for Luzern - Zurich.

(Note that depending on when your flight is you do not need to spend the last night in Zurich. I live in Wengen and travel a lot for work, and if my flight is after 11:00 I just take the first train from Wengen in the morning. Only if my flight is earlier do I stay overnight at the airport.)

I was in the process of suggesting the discounted (advance purchase( Paris to Gimmelwald ticket plus 4-day Berner Oberland Pass yesterday when Inwas called away to leave for an important occasion before I could confirm the savings. Now I see WengenK has suggested the same thing.

I did get as far as confirming that the advance purchase as one through ticket on SBB (the date I used was 2 months in advance) would qualify the Basel to Gimmelwald for the “international ticket extension” rate of 43,90 CHF, which is much less than the 2 extra “pass days” on the BO Pass (needed if you want to cover that day’s journey) would cost. A 4-day pass will fully cover your time in Wengen and the travel to z Luzern on Day 4, so that is all you need.

However, it will not fully cover the Schilthornbahn above Gimmelwald, nor the pricy Jungfraujoch journey above Eiger Gletschergarten station. See the coverage map:

https://www.berneseoberlandpass.ch/assets/Uploads/BLS-BO-Pass-M-23-WEB.pdf

The Schilthorn cablecar is covered at 50%, and the Jungfrau train has a “special price” which I suspect is 25%. A Half-Fare card will cover 50%, but it is not worth purchasing that for 4 people for the minimum benefit it confers. And actually I suggest you skip the Jungfrau trip. In my mind it is overrated and overpriced. Once past Eigergletscher the train enters a tunnel through the rock of the Eiger and does not emerge. You arrive at the “Top of Europe” in the tunnel and take an elevation up to the building and viewing platforms, or the door to go outside into the snow. It might seem adventurous to some, but I think kids the age of yours would find it boring—-especially after the exciting Schilthorn experience.

What I I suggest instead is a visit to Grindelwald for the Firstbahn activities—-zip lines, mountain coaster, or Trottibike (my kids favorite).

https://www.jungfrau.ch/en-gb/grindelwaldfirst/

You could combine this with the famous scenic walk from Männlichen to Kleine Scheidegg, which is highly recommended. Your day would look like this:

Cablecar plus bus, from Gimmelwald to Lauterbrunnen, train up Tom Wengen, cablecar up to Männlichen (consider paying the 5 CHF extra for the “Royal ride” on the roof)

https://www.maennlichen.ch/en/summer/experiences/royal-ride.html

Then the eas hike to Kleine Scheidegg, continuing up to Eigergletscher station (by train or walking). Then ride the new E press gondola down to Grindelwald Grund and walk through town to the First Gondola. Spend the rest of the day with the activities there, then return to Gimmelwald by the valley route ( train from Grindelwald to Lauterbrunnen).

All these lifts and trains are fully covered on the Berner Oberland Pass. Extras would be the First activities, and lunch. Our lunch spot this day was the deck at the mountain restaurant at Bort, a station partway up the Firstbahn. That was great. But there are lots of other opportunities.

Gimmelwald is really tiny, no grocery store and few restaurants. I would recommend staying in Murren, about 30 minute walk uphill , which is still car-free but has a Coop grocery store and restaurants. (Of course, many folks here also like lodging in Wengen.)
It's easy to train to the Zurich airport from Lucerne, so if your Zurich flight isn't too early, spend your last night in Lucerne.
A agree , second class rail on Swiss trains is very nice, no need for first class, IMHO.
Have a wonderful trip in this incredibly beautiful country!
Safe travels!

Thank you everyone! Very helpful and points me in the right direction.