How to Use Jr Travel Cards when Buying Advanced Train Tickets?

If I want to buy train tickets online now for certain popular trains (i.e., Golden Pass Luzern-Interlaken Express), do I just buy 2 Adult tickets, and make 4 seat reservations? I just want to make sure the 4 of us can stay together!

The Luzern-Interlaken Express is just the regular hourly train between Luzern and Interlaken. Since it just shuttles between these 2 cities (and stops in between), If you board it early at either departure point, you will have your pick of seats. I tried, and when I try to reserve seats on this train, I get the message, "seat reservation not possible". Note below says seat reservations are available on IC and ICN trains only. The Luzern Interlaken Express is an IR train.

Generally, only special tourist trains like the Glacier Express, Bernina Express, Gotthard Panorama Express, require seat reservations bought directly from the operator.

Add up the cost of all your full fare tickets. If it is more than 240 CFH per adult, then the 30-day Half Fare Card, costing 120 CHF per adult will save you money. Then you can get the free family card.

In Switzerland it is impossible for train tickets to sell out. Trains are mass transit, used by people to go about their daily business, and having to contend with suddenly not being able to return after a day of shopping in Luzern is not something the Swiss would put up with. Is if a million people where to rock up to Luzern station and ask for a ticket to Interlaken they would all get one. And we would be talking about it for years probably...

So these are normal, mundane, commuter trains basically. Commuter trains with scenery, and you can just buy a ticket at the station, or from a ticket vending machine, or your phone app, all up to the moment you travel. As long as you have your ticket before you board.
And with the junior card the kids do indeed not need a ticket.

But have you looked at the Half Fare Card? It comes with the family card for free, and this gives your kids free travel as well, and gives the adults 50% off, and that not only for normal, trivial public transit, but also for mountain railways. Costs 120 per adult, and may be worth it for you.

Thanks Sam. I'm wondering if this is the same Luzern-Interlaken Express? I followed the Golden Pass website link to buy tickets, and it directs me to:
https://journey.mob.ch/en/routing?_ga=2.28196284.1010496725.1652232695-1128375332.1652232695
At the MOB website, it refers to "Luzern-Interlaken Express" with codes WR (Restaurant), PA (Panorama Coach), R (Place Reservation possible). Does that mean all the Luzern-Interlaken Express trains have these features? Or only certain coaches on the line are the Panoramic coaches that I have to buy through MOB? Sorry, this is super confusing!

Great point about the half-fare card - I thought those were only for Swiss residents!

The Luzern - Interlaken trains are all operated using Adler trainsets. So all trains are the same. Most seats have panoramic windows, and there is a restaurant. One thing to watch out for is that on busy days they couple another 3 cars to the train, but you cannot get to the restaurant from these cars, so pay attention where you board if you want to visit the restaurant.

These trains are used by locals commuting to work, children going to school, people of to Luzern to go shopping. So taking them is not complicated.

Thank you WengenK! That is very helpful! :)