Swiss train pass and Berner Oberland Pass

I'd go for first class in your case. The cars in 2nd class do get crowded in the popular areas and 1st is usually empty. You don't need a BO pass if you are getting the STP and you are not going to be spending a lot of time riding all the lifts and cogwheel trains up to mountains in the BO area and just spending time in Grindelwald.

For my last couple of trips, I have purchased the 1st class Swiss Travel Pass and have found the additional expense well worth it. Less crowded trains and more room for luggage.

I was just in Switzerland last month. You might find my trip report helpful:

https://community.ricksteves.com/travel-forum/trip-reports/solo-in-switzerland-june-2024-my-trip-report

Make sure you have your passport handy on the trains as you may be asked for ID with the Pass. On past trips, a photo copy of my passport was accepted, but one conductor on my recent trip wanted to see my actual passport.

Have a great trip!

Thank you for your quick replies. While in Grindelwald we will be visiting the different sites and cities. Do I need the Oberland pass plus the STP pass?

No, don’t get the Oberland Pass. The Swiss Travel Pass will cover you up to the mountain towns of Wengen and Murren. If you go higher than that, Schilthorn for example, you can just purchase a ticket. Show your Pass and you will get a discount.

If you click here and scroll down, you can see all that the Pass covers and what discounts you can expect:

https://www.myswissalps.com/travel-ticket/swiss-travel-pass/

You do not "have" to buy any pass. You can always just buy tickets at the ticket office of the cable car or mountain railway you want to take. With the STP you get 50% off in most cases.
The Berner Oberland pass has a lot of overlap with the STP, so a bit of overkill. The HFC/BO pass combination is a good one though.

Thank you for your help. I will just buy the STP and we should be good for our vacation in Switzerland. Can’t wait for September!