Welcome to My Swiss Alps.
I have the same concerns on longer hikes; most of the ones I take these days are shorter not problematic. Although, on the three to four hour walk from Hohtenn to Ausser berg in the Rhone alley, I am quite pleased to find a beer garden with toilets about half way. ;-)
For both the beer and the toilets.
In the area that you mention, not surprisingly, it depends on the trail. ;-)
Pick your trails to have restaurants or train/cableway stations or inns at each end....that is pretty easy. Some trails have facilities along the way ....for example, a restaurant at Winteregg between Mürren and Grütschalp. Free standing toilet facilities are not common.
To go beyond that level of detail, I, at least, need to know which hikes you will take.
If I were trying to find out more, I'd look at a couple of places on the internet. I hope there are better ways, because these are not the most direct answer to your question.
This list of hikes:
www.jungfrau.ch/en/tou rism/destinations/klei ne-scheidegg/hiking-trails/
a map which shows accommodations and has images showing likely buildings along a hike.
Here is one:
map.search.ch/Grindelw ald,M%C3%A4nnlichen?poi=bergbahn,gastro,ha ltestelle,zug&x=-3455m&y=-3347m&z=128
I have centered it on Winteregg, and used the menus under "Points of Interest" to open Traffic and Gastronomy"
Zoom way in for detail, and switch back and forth between aerial and map view. With sufficient magnification, you can see the tables with umbrellas.
I hope someone has a better way.