Help needed with itinerary for 6 nights in Switzerland

Niz, you don't say when you will be doing this, what time of year, and that partially affects the answer.

To answer the last question first, a pass will almost certainly be good value, especially as you are almost certainly doing local trips from Luzern and Wengen.
You do not need a car, all this can be done better by train, and you cannot get to Wengen by car, train only.

If you are travelling in winter, it will be all snow. If you are travelling in summer, you have to go up a mountain.
A good day trip from Luzern is Titlis. Website: https://www.titlis.ch/en You take a train from Luzern to Engelberg, then a series of cable cars to the top. The summit is above 3000m. It has a small glacier on top and plenty to do. See the website for details.

From Wengen there are lots of trains and cable cars further up the mountain, a Swiss Pass will give you a discount on these.

The Golden Pass train is a marketing name for the rail route Luzern - Brünig Pass - Interlaken - Montreux. You will be travelling on the first half when you go from Luzern to Wengen (via Interlaken), and on the second half when you go to Lausanne.

The other two marketed routes (Glacier Express and Bernina Express) involve going to South-East Switzerland, which is out your planned area. You will see plenty of scenic around Luzern and Wengen.

This is the leaflet and map showing where the Swiss Pass is valid, hopefully it will help: https://www.sbb.ch/content/dam/sbb/de/pdf/freizeit-ferien/ferien-kurztrips-schweiz/internationale-gaeste/sts-geltungsbereich.pdf

Which pass will be optimum value for money for us? or is it better to
rent a car and take train rides and back to destination? First time to
Europe, many questions and our flight booked for this week.

Public transportation will be the easiest and cheapest way to go. The Half-Fare Card is likely the most economical rail pass option. It gives you 50% off any form of transportation for 30 days (trains, cable cars, boats, buses, city trams, etc.). Get the family version which will allow your kids to travel free as long as they are with a parent. If they are not with a parent while traveling something has gone wrong!

How do we accommodate scenic train rides in this itinerary? we would
like to do Bernina Express, Golden Pass, Glacier express and any
other. All or some of them.

You can take the Golden Pass from Luzern to Interlaken on the day you are going to Wengen. You can rejoin the GP train later in your trip the day you go to Lausanne by taking the GP from Interlaken to Montreux.

The other scentic trains are out of the way for your itinerary. Besides, on a beautiful day you will want to be up in the mountains and not stuck on a train!

Sorry Chris, I thought I mentioned that. We will be coming to Switzerland between to 18th to 23rd May. I have confirmed booking in Wengen between 20th to 23rd May which I can't cancel. Coming from Munich on 18th and going to Paris on 24th May.

Thanks a lot. As we are travelling in third week of May, would there be any snow to see in Wengen but I want to see Spring also. It might sound like a paradox but I want to see beautiful villages in Spring but my kids can't stop talking about snow. So keeping my original plan of Munich to Lucerne (2 nights there), Lucerne to Wengen (3 nights there) and Lucerne to Lausanne (1 night before heading off to Paris), do you think we would get to experience, snow and Swiss alpine though we won't get to do Bernina Express or Glacier Express.

Is there anyway to accommodate Bernina express if we go to another place from Munich instead of Lucerne or another place from Wengen instead of Lausanne?

Thanks a lot. As we are travelling in third week of May, would there
be any snow to see in Wengen but I want to see Spring also. It might
sound like a paradox but I want to see beautiful villages in Spring
but my kids can't stop talking about snow.

It is not likely going to snow while you are there, but the mountains will still display plenty of snow. Excursions up to the Jungfraujoch or Schilthorn will definitely show them snow! Check out the SwissPanorama and Gimmelwald webcams (when it's daytime over there).

You may also consider mountain excursions while you are in Luzern. Mt. Rigi, Titlis, and Pialtus are all easy day-trips to do from Luzern.

Is there anyway to accommodate Bernina express if we go to another
place from Munich instead of Lucerne or another place from Wengen
instead of Lausanne?

So keeping my original plan of Munich to Lucerne (2 nights there), Lucerne to Wengen (3 nights there) and Lucerne to Lausanne (1 night before heading off to Paris)

Niz, I assume you mean Wengen to Lausanne!
Spring has arrived, most of the snow will have melted in Wengen, though it has turned cold in he last week, so maybe they have had a little, but (in Wengen) it should all have melted by the 20th May.
But, from Wengen you surrounded by spectacular mountains which have snow on top even in the summer. If you have a good weather day, and a lot of money, you can go up the Jungfrau.
And from Luzern you can also go up Titlis and your kids can play in the snow.

If you look at the map I posted last time ( https://www.sbb.ch/content/dam/sbb/de/pdf/freizeit-ferien/ferien-kurztrips-schweiz/internationale-gaeste/sts-geltungsbereich.pdf ), the Bernina Express runs from Chur (right side of map, south-east past St Moritz to Tirano in Italy. You would have to go Munich, Zürich, Chur and end up in Italy, totally the wrong direction.
The Glacier Express runs from Zermatt to Chur, still the wrong direction.
But, you will be doing the "Golden Pass" route, and seeing plenty of mountains.

Thanks FastEddie, next question is Swiss Half Fare Pass or Swiss Pass or no pass, just book the tickets point to point. Also, do any Swiss pass have discount for travel from Munich and travel to Paris? I googled and checked the websites of GoEuro and Eurail. They give totally different prices for the same trip from Munich to Luzern.

Yes Chris, it's Wengen to Lausanne.

Thanks Chris, so I think I will stick to my original plan of Luzern - Wengen - Lausanne. Next question is which rail pass and is any Swiss pass useful for Munich and Paris trains?

Don't worry about scenic train rides - with your itinerary, you will be IN the scenery!

As said above, from Luzern, you can see Mt. Rigi, Mt. Titlis, or Mt. Pilatus (you'll have time for one). I did Rigi, so I can't compare them, but again, it was very scenic; you take a boat to and from the mountain and a train ride up.

From Wengen, you can take the train up to the Jungfraujoch, or the train down to Lauterbrunnen and the cable car up to the Schilthorn. Once you are here, you'll see that you don't need to do anything "special" to see beautiful scenery - it's all around. You are in the Alps - literally surrounded by mountains - so this is the "alpine experience" you want.

Lausanne doesn't have nearby mountains, but is near very pretty Lake Geneva as well as Chateau de Chillon (a castle hundreds of years old and never conquered so it's intact).

Don't worry about taking "scenic trains" that will take you way out of your way. Instead, enjoy the beautiful scenery where you are (and you've chosen very scenic places).

Swiss Passes only give discounts in Switzerland, i.e. from and to the border. Munich to Luzern via Zürich, you pay full price until the first Swiss station (St. Margrethen) and the pass is valid from there. Similar from Lausanne to Paris.
But, depending on which pass you get and whether you have a free day you may not have a "spare" pass day for Lausanne to the border.
You need to book these tickets ASAP. The prices go up the nearer the date. Especially the TGV to Paris, do not leave it another day.

"I googled and checked the websites of GoEuro and Eurail." - wrong websites. You need to go to the actual rail companies.
Swiss Railways ( https://www.sbb.ch/en/ ) is currently offering Lausanne to Paris:

Lausanne - Paris-Gare de Lyon
Wed, 24.05.17, 12:23 - 16:03 Hour
Duration: 03:40, 0x Change(s)
CHF 103.00 per person

The cheaper tickets have already gone.

Thanks FastEddie, next question is Swiss Half Fare Pass or Swiss Pass
or no pass, just book the tickets point to point.

The Half-Fare Card will probably be the most economical option. Check out my comment above.

Also, do any Swiss
pass have discount for travel from Munich and travel to Paris? I
googled and checked the websites of GoEuro and Eurail. They give
totally different prices for the same trip from Munich to Luzern.

I'm a little fuzzy on that. I know your Lausanne-Paris ticket will be eligible for a 50% discount on the Swiss segment if you have the HFC. I don't know how that works (if at all) on the Munich-Luzern segment.

Thanks Chris. One last question, I have decided to get the half fare card and I want to buy that before I book the Paris ticket TGV. I am again at different websites, which one is the right one?
https://shop.swissrailways.com/basket.php - Euro 224
http://www.raileurope-gcc.com/spip.php?page=sales&re_domain=cart&re_oper=travellers - Euro 220

Or else, the site which you provided earlier?

Thanks Harold, that's reassuring

Niz, you do not need to buy your ½ price pass before you buy your ticket. You just need to buy it before you use your ticket, and show it together with the discounted ticket to the ticket inspector on the train.

Always go to the company running the trains. Raileurope is a reseller operating in North America.
SBB is currently offering the following prices:

Lausanne - Paris-Gare de Lyon, Via Genève, Fri, 26.05.17, 10:47 - 14:52 Hour, Duration: 04:05, 1x Change(s)
CHF 87.00 per person, 2nd class with a Swiss ½ price card.

Lausanne - Paris-Gare de Lyon, Fri, 26.05.17, 12:23 - 16:03 Hour, Duration: 03:40, 0x Change(s)
CHF 76.00 per person, 2nd class with a Swiss ½ price card.

Sorry Chris, I am a bit confused, how would I buy the Lausanne - Paris ticket without the Swiss half price card, if I want to make use of the Half price? Won't I be asked to make the payment while I purchase the ticket for Swiss Paris train? Also the delivery of the half price card via email is valid, isn't that right?

I don't see a online delivery option from the official site. https://shop.swissrailways.com/basket.php
what do I do?