Welcome to My Swiss Alps!
I can see that you have done some homework on your travel options.
This will help you with many of the details:
With the Swiss Travel Pass the train via Zweilütschinen is the cheapest and least scenic route to Lauterbrunnen (36 minutes, twice per hour) and the extension via bus to Stechelberg is also free. The cableway and train from LB to Grütschalp and on to Mürren is also free. Study the key at the upper right in the validity map carefully, some of it is tricky, and zoom way in to see the details near LB.
cdn-doc.myswissalps.com/do cs/default-source/rail-network-maps/swisstravelsystem .pdf?sfvrsn=7788603a_34
Those are subsidized public transport between population centers, as is the train from LB to Wengen. All others are private excursi0n rail lines and cableways and do not get the benefit of the government/SBB subsidy. If you are going to do a lot of cableways, the half-fare card often is a better option than the STP in that region.
This is also worth a look:
Up and over by cableways to Wengen and train to LB is a lot more fun than the trip through Zweilütschinen, but has a few connections which can slow you down, and is similar in time to the 1 hour 33 minute 3rd option- excursion train via Kleine Scheidegg to LB ( only partial fare discount; although the fare from Wengen to Lauterbrunnen is free with STP).
These maps will give you details of the routes; I have zoomed the Mapsearch map in to zoom level 32, at which the transport services become clearly visible:
This one give altitudes and is topographic:
map.geo.admin.ch/?topic=ech&lang=en&bgLa yer=ch.swisstopo.pixel karte-farbe&layers=ch.bav.ha ltestellen-oev,ch.swisstopo.swiss tlm3d-wanderwege&layers_visi bility=true,false&E=26 37889.83&N=1161423.54& zoom=5
If you use the timetable, taking advantage of the "via" option of Männlichen. Zweilütscinen or Kleine Scheideg, you can understand the times and the time of the last trip down from Schilthorn and around to Grindelwald. Cableways stop running in the evening before the trains via Zweilüutschinen.