Hi IbnEBatuta- Still answering in pieces.
To better understand Annika's comments and mine, I suggest that you refer to the timetable that she linked, as well as this map:
map.search.ch/?pos=633344,105728&z=2& poi=bergbahn,haltestel le,zug
Turn off the icons for transport stops in the menu. Zoom in to see the train lines.
However, the trip from Interlake to Zermatt is straightforward. Faster via the new "Lötschberg Basis Tunnel to Visp", and slower by about an hour or so via the much more scenic historic old route up to kandersteg, through the old shorter tunnel, and down the side wall of the Rhone Valley to Brig, then to Visp and on to Zermatt.
You might consider putting the stay in the Bernese Oberland near the end of your trip, then finish off by going to Zermatt and taking the Glacier Express from there.
Annika has outlined a few good choices, each one is a nice trip.
Whether or not to visit CERN, or the Alps, or the cities, or museums, or lake boat rides is completely a matter of personal preferences, taking into consideration the ages and interests of your party. In the case of the Alps, also, the weather and season of the year. It is hard for us to make those judgements for you. Searching in My Swiss Alps website can lead to information about those items that can help with your decisions.
A simple example- I would like to go to CERN sometime, as well as Fort Cindey. My wife is not interested.