Swiss tickets/Pass and routing help.

Jungfraujoch is expensive. I would make sure to check the mountain video prior to committing . Typically, mornings tend to have better weather for most mountains. Schilthorn has some James Bond exhibits that were fun. There was a Bond movie filmed at Schilthorn and Murren. The Swiss Travel Pass covers part of the Schilthorn trip. Sometimes the weather can be clear on Schilthorn and not Jungfraujoch and conversely. The Swiss Travel Pass covers Mount Rigi as well. The small, but worthwhile art museum in Luzern is also covered by the Swiss Travel Pass as is the Panarama painting.
We did the Bernina Express via a panoramic train. We also did the Golden Pass route on a regular train. I recommend pricing out the two types of trains to determine if the extra expense of the panoramic train is worth it.
Have you researched the Berner Oberland cities? Grindelwald was a little touristy for me. Murren and Wengen, absolutely charming. Gimmewald, charming as well but quite small. We stayed in the Lauterbrunnen valley which is lovely and worked well for us.

If you're set on doing Jungfraujoch and you get a good weather day (check webcams that morning before buying tickets) AND you like easy walking/light hiking do this:
Grindlewald > Mannlichen > Panorama Hike to Kleine Scheidegg > Jungfraujochbahn (roundtrip from Kleine Scheidegg) > train to Wengen > walk around Wengen, possibly for dinner > return to Gimmelwald

Some other great activities we enjoy every year in the area: ebiking Lauterbrunnen Valley, North Face hike from Allmendhubel (Murren) to Gimmelwald, Schilthorn, Schynigge Platte, Lake Thun (with stops at Spiez, Oberhofen & Thun) or Lake Brienz boat tour (with stops at Giessbach and Brienz)

Probably get the Swiss Half Fare Card, and buy tickets as you go. And do not worry to much about scenic routes. If you are not used to train travel in Switzerland you will find every route scenic.

The best way to do the Jungfraujoch trip is, in my opinion, to do a round trip: Go up via the Eigerexpress, and come down by train via Wengen - Lauterbrunnen.

Lastly: Why does everyone want to visit Vaduz, the most boring village in the most boring country in Europe?

Not “everyone” wants to visit Vaduz. Only the people who want to check another country off their list. Which doesn’t include me or anyone I know.

I would suggest the order of your travel be Luzern first, then Grindelwald, then Zermatt. Then if you really want to set foot in Lichtenstein, you would take the fastest route from Zermatt to Zurich (3.25 hours, one or two changes on the way). Then, at least according to my limited research, you take a train to Saran’s and catch a bus to Vaduz from there.

Whatever you choose, given that you want to include the Jungfraujoch train, a Half Fare card would be worth the cost, as it applies to all your transport options, and gives the greatest discount on the Jungfrau ride (50%rather than the usual 25% with other passes).