Hi, 2travelers -
Welcome to the forum.
You have been working hard at planning, as is evident from your comments.
With a short trip such as you have, using the "named" excursions in off-season (if available) might not be the best option. And, you have picked some possible places that require a lot of travel.
If you want to do them, use the timetable to figure out times and also look at maps. And, you do not have to use "named" excursion trains. Often, there is a "regular" train, with the same scenic views through slightly smaller windows on the same route.
You'll get a sense of time and distance.
Luzern, by itself, offers a lot of different scenic options. You could easily spend a few days there and nearby , even in normal grey, cold winter weather. Even better if you have sunshine. You don't have to select only the cograil to Pilatus. You can go up the back way, via Kriens, for example
Zürich is my favorite city in Switzerland, but it is not "once and done" for tourists. Takes some time... it is bit more subtle. Took me 10-15 years of visits before could say what I just said. Stiill, there are nice things for a day trip, but not as varied or scenic as Luzern.
Apart from specific places and train routes that you have researched, do you have particular personal interests? The Olympics Museum in Lausanne?
Hiking, trains, museums.....?
The famous places are famous for good reason, but there are a lot of really nice less famous places in reach of Lausanne.
I have just posted series of places worth visiting north of Lausanne. You might consider visiting some of them, as one option. Perhaps your son knows them?
Take a look at ALL of this thread:
Trying to see the famous places in Switzerland in cold weather, between seasons when many services are shut down ( not to mention, resort-area hotels), is not an easy task. Starting from Geneva, instead of Zürich makes it harder.
I know...used to work in /near Geneva.
Luckily, the Swiss travel network gives you a lot of options, and, pleasantly, you can work on them via internet before you go.