Jan 28, 2019 - 4:22 AM
I agree with the others that doing both attractions in the one day is over ambitious - although not impossible. It would be more like an endurance test than a pleasant experience.
In June 2015, my partner and I spent several enjoyable days based at Unterseen (near Interlaken) and using the Berner Oberland Pass.
We included the Schilthorn trip and had a lovely day. The weather was magnificent. Compare that to my "effort" in June 1989 when we didn't get any further than Murren due to bad weather.
On different days we took boat trips on both lakes, Brienz and Thun. Easily combined with scenic bus and cableway trips using the Berner Oberland Pass.
My though is that it's better to spend more time in fewer "areas" but we are all different. This is a wonderful site and you'll find the resources you need or links thereto.
Enjoy your planning - and your travels.