Which Swiss Rail Pass suits my trip best?

Question 1 : Are there any direct trains? We have been looking and it seems we’ll need to change trains 3 times.

There are no direct trains. One change from Geneva airport to Zermatt, 3 changes from there to Grindelwald, 2 changes from there to Zurich. The reason is that the trains from Visp to Zermatt and back, and the trains from Interlaken Ost to Grindelwald and back are meter gauge tracks with cogs engaged for climbing steep sections. The rest of the trains are on standard gauge tracks.

Full fare tickets for GVA to Zermatt: 102 CHF, Zermatt to Grindelwald, 94.20 CHF, Grindelwald to Zurich, 62.20 CHF if you take the slower, more scenic route via Luzern. The faster, less scenic route is 81.20 CHF.

Buying 2 1-month Half Fare Cards for 120 CHF each, plus getting the free Family Card will allow the 2 15-yos to travel with you for free. Then all the prices quoted above will be half of that, plus all of the mountain lift and railways taken will also be 50% discount. That will be your lowest cost. Passes almost always cost more.

PS. rather than going from Grindelwald to Zurich, then flying to Venice, you could go by train from Grindelwald in about 7 1/2 hours and 3 changes. Total travel time would be about the same and you could spend more time in the mountains rather than Zurich. The Half Fare Cards and family Card will give you the discounts as far as Domodossola, Italy.

Thanks !!!
Car rental vrs train question :

I prefer to travel by train but husband wants to rent a car ....

The rental car logistic is complicated:

Since we will be in Chamonix, we have 2 options:

1-) returning car in Chamonix and then take train to Tasch /Zermatt (3 trains !!)
2-) returning car in Geneva airport French side (this way the drop off won’t cost a fortune !!) and then take the train from Geneva to Tasch/Zermatt .

I have read over and over that there is no point in renting a car in Switzerland, just wanted to make sure (that based on our itinerary) what are your thoughts about it?

Chamonix-Geneva drop off car
Geneva-Zermatt
Zermatt-Jungfrau Region (Grindewald will be our base city)
Grindewald-Jungfraujouch and back
Grindewald-Lucerne
Lucerne-Zurich

We already bought tickets from Zurich to Venice so the train suggested all the way from Grindewald is not an option but we really appreciate you mentioned it :-)

Happy day :-)

Car vs train.
For one thing, the car will sit in a paid parking garage at Taesch at 16 CHF per day while you are in Zermatt.
I don't know the parking situation in Grindelwald. You may have to pay to park depending on your lodging. Check that out.
You really should not hang on to your French rental car to go to Switzerland. Turning it in at Zurich Airport will come with a huge international drop charge because the car will then have to be transported back to France before it can be rented again. A minor point is that you would need to purchase and attach a Swiss vignette costing 40 CHF.

Since the train ticket cost is less, and the travel time is similar, turning the car in at Chamonix will save a lot of time driving to Geneva to turn the car in.

Finally, train changes are nothing to worry about. They are designed as part of the system. It is not like changing planes at the airport. The 3 changes from Chamonix Mont Blanc to Zermatt are like this. You change trains at Vallorcine because the French train is not compatible with the Swiss tracks. Your train will be waiting for you and when everyone has made the change, the Swiss train will depart to Martigny. At Martigny, you change from meter gauge to standard gauge train to Visp. At Visp, change back to meter gauge train to Zermatt.

Many many thanks !

Sam, when you say that "the train will be waiting for you", let's not imply that one can take their sweet time, right?! 😉Folks need to be ready with luggage to get off European trains as soon as they stop, know your platform numbers, and move at a steady pace.

Regarding Venice, most folks don't take more than one gondola ride, as the rides are short and pricey. Perhaps you meant vaporettos ( the water buses)? Instead of a gondola ride, I recommend Row Venice, where a group of four can receive rowing lessons on the back canals, 90 minutes, about 90 Euros total ( pre-COVID.)

Safe travels!