Another advice I need is the transport from montreux to London? Surfed n mostly are trains n they are expensive! Any idea if there are any overnight bus to London?>

Probably cheap flights are cheaper than going by land - if there is a bus check Eurolines - the pan-European bus service which however does not run nearly as comprehensive routes as trains do but perhaps?

https://www.eurolines.com/en/

Or go to www.skyscanner.net or www.whichbudget.com to see if there are any cheaper flights from any Swiss airport.

Well it does not look like Eurolines serves Switzerland at all! If I read the info right.

Yup.. The furthest they go is geneva if I'm not mistaken..

Still not able to find our way to London yet. Guess we still need to search more or change our last venue to another city with bigger airport

Another question, for this itinerary, is it advisable to get a 8 day swiss saver pass for 3 of us or to buy tickets for each destination?

I'd say the 8-consecutive-day Swiss Saver would be a great deal since you are traveling nearly everyday and all around the country (which is fine - I do it all the time!) - if you know exactly what you will do on trains then you can figure out if ordinary tickets are cheaper or the Half-Fare Card (costs about $135 to buy then you get half off everything - trains, boats, gondolas, etc.

But I think with that much travel the consecutive-day pass would be best and you never have to wait in lines to buy tickets, etc. And I with such a pass always end up traveling more than I think - like on Lake Thun with a pass you can jump off one boat and take a bus or train - or if your days in the hills are wet you can day trip to some nice city that is bearable in wet weather, etc.

If the sum of tickets or Half-Fare thing even approaches the cost of a pass go for the pass - never wait in line and you may travel more than you think.

For your journey Montreux-London, there are plenty of flights from Geneva airport to London so perhaps a train Montreux-Geneva Airport (there is a direct train, ie no changes) every 30mins or so) taking around 1hr15m, then a flight with either British Airways to Heathrow or Gatwick, EasyJet to Gatwick - easier transport for you than Luton or Stansted, and even Swiss Air may have some deals this far out.

If visiting any museums or site like the Chillon castle then a Swiss Pass gives free entry to 400+ museums and sights (not sure Chillon is on it) - but only on days of 100% travel - so with a flexipass it would only be on the days you use it for 100% coverage - so if going to any museums in Bern (Paul Klee one there is astounding), Freiburg, Montreux, Vevey factor in about $15-20 a pop for museums the pass would cover. But not many folks go to Switzerland to see museums!

As per your advice, Swiss saver pass for all of us then. N we shall travel to geneva to get our flight out to London. It seems that Swiss airline offered best price to heathrow airport