Hello Lisa R.
The GA, as the Swiss Travel Pass, are valid to inhabited places only. With a very few exceptions, such as Mt. Rigi, the GA travel card does not offer any free travel on mountain transportation, no matter being mountain train, cable car, chair lifts, etc. For these, you will have to pay extra.
When you will primarily stay in the Berner Oberland, the Berner Oberland Pass might be another option. It works well with the Swiss Half Fare Card.
https://www.berneseoberlandpass.ch
In order to give you better advice, you should list your itinerary in detail. What are your bases? O I am sure there is some potential for optimisation, too. My personal advice: finish your planning first, then bother with tickets. The ticket selection & purchase should be your very last step of your entire planning process.
If you need more help with planning your trip, for example if you are unsure which places to visit (for example, I personally would skip Kandersteg), check the TripAdvisor Switzerland travel forum, there you will find a lot of advice from locals on what to see & visit: https://www.tripadvisor.com/ShowForum-g188045-i336-Switzerland.html
Here, on this platform, we are the ticket experts.
Kind regards,
Roland