Help! Where to start/ end and use of rails

yes, all those are easily connected by train - comfortable and frequent.

Is this your first trip to Europe?

No it's not.. had traveled all over Europe but really didn't use much rails except when we were in between Bergen and Oslo, Norway.
Thank you for your response. I will have to check where the stations are before I book our hotel or bnb because I don't like to be far from train stations

Geneva and Zürich both have very comprehensive bus and tram systems, and several subsidiary train stations so you don't need to be at the main station. Both also have train stations right at the respective airports.

Interlaken (with two train stations, Interlaken West for the west of the the town, and Interlaken Ost for the east and for the trains up into the mountains, the boats on Lake Thun go from Interlaken West, the boats on Lake Brienz go from Interlaken Ost, both just a few feet from the train station) is really primarily a transportation hub with several large old - very old - hotels from when the mountain area was just starting to attract tourists. Lauterbrunnen and the two sides of its valley with Wengen on one side and Mürren on the other are actually up in the mountains although only 20 minutes from Interlaken Ost down at lake level. If you have a look at the Rick Steves Switzerland book you can see all the mountain transportation around the Berner Oberland as the area is called, including to get from Lauterbrunnen via Wengen (or for Grindelwald on the new gondola) up to Jungfraujoch. Also how to go from Mürren up to the Schilthorn of James Bond fame.

Thank you for your detailed response.
So basically if for example we are staying 3 nights in lauterbrunnen , we can go to
jungfraujoch for a day trip and do murren and OR grimmewald on another day using lauterbrunnen as our base

You don't need to be in Zurich if you're flying out of it. Stay in Luzern instead as easy one hour train, which goes directly into the airport.
Add as many days as you can to your trip- you won't regret it.
I'd maximize your time in the Berber Oberland. You can't relax with three nights, which is two full days. No one is ever ready to leave. Stay in Wengen or Murren.
And- weather dictates all in the mountains. More days increases your chances of good days.
The Swiss train system is world class, user- friendly, and a joy.
Have a great trip.

Thank you Pat
I was just checking the possibility of visiting both Murren and Jungfraujoch from Lauterbrunnen but I' think thats a lot to do in 1 day...i can definitely add 1 to 2 days around that area as you suggested...I've booked a hotel 2 months ago in lauterbrunnen x 3 days but I think I would need to stay maybe in Murren after Zermatt (for 1 night) and just do Jungfraujoch by itself in 1 day with lauterbrunnen as our base.
So from Geneva to Zermatt to Murren then lauterbrunnen and yeah Luzern/ Zurich
Thank you again

If you wind up staying in or near Luzern, the train ride, cogwheel, over the Brünig Pass between Interlaken Ost and Luzern, change ends in Meiringen (Reichenbach Falls of Sherlock Holmes fame is near the station) is exceptionally scenic. Leaving Interlaken Ost try to sit on the left side. When you change ends in Meiringen just flip around but stay on the same side.