2weeks in Switzerland

Hi and welcome to the forum.

Think about renting a car twice! You'll have plenty of trouble parking it anywhere, even in villages such as Lauterbrunnen and Kandersteg, you can't bring it to Zermatt, you would have to leave it down in Täsch, paying for parking, taking the train up to Zermatt anyway. So, the solution is The train !

You're backtracking the way you're planning. Better try to do this itinerary (by train):

• Zurich - Berne - Interlaken - Lauterbrunnen (Or, more spectacular: Zurich - Lucerne - Brünig pass by cog railway - Interlaken - Lauterbrunnen)
• Lauterbrunnen - Interlaken - Spiez - Zweisimmen - Montreux (Golden Pass Route) - Zermatt.
• Zermatt - Brig - Furka tunnel - Andermatt
• Andermatt - Göschenen - Bellinzona - Lugano

Come back with further questions, it's a pleasure to assist

If you want to travel by car, don't go to places where the road ends like Lauterbrunnen or Kandersteg (no circular trips possible, only expensive railways/cableways from there up into the mountains) or where cars are not even allowed to enter (Zermatt).
For a car trip, choose an itinerary like:
Zurich - Einsiedeln Monastery - Schwyz - Weggis - Lucerne - Brunigpass - Ballenberg Ecomuseum - Aar Gorge - Handegg Gelmerbahn - Grimselpass - Gletsch steam train - Betten (cableway to Bettmergrat and back, may be combined with some hiking or a stay at Bettmeralp) - Brig - Simplonpass - Verbania Pallanza (boat trip to Isola Madre and Isola Bella) - Locarno - Bellinzona (castles) - Lugano - Menaggio - Chiavenna - Soglio - Malojapass - St. Moritz - Berninapass - Livigno - Foscagnopass - Bormio - Stelviopass - Spondinig - Mustair Claustra - Pass dal Fuorn - Fluelapass - Davos - Lenzerheide - Zurich
Google for these places; there is a lot to do and to see

Thanks so much for your replies...am researching a little more on my trip and will come back if I have more questions...which is fairly certain I'd say:)
Thanks again