>> We (self, wife and 2 daughers-13/10yrs) will be traveling to Switzerland from May 18-25 ... based at Grindelwald only for the entire duration of 7 nights ... We would reach Grindelwald by 18th evening and will need to check-out by 25th morning
Your plans look pretty good on the whole. I have some comments about a few of your days.
>> 20th – We have friends in Bern. We are discussing, (being Saturday) possibly they will come down to Interlaken and we plan to do Lake Brienz cruise
As Luzern does not really feature in your plans, why not kill two birds with one stone by meeting your friends in Luzern and spending the day with them there, perhaps doing a cruise on the Vierwaldstättersee (Lake Lucerne)? You would also get to travel on a sector of the Golden Pass route, over the Brünig Pass and along several beautiful lakes. (Although you may have done this sector already, on your way to Grindelwald.)
You could save the Lake Brienz cruise for any spare time you have during your stay in Grindelwald, due to poor weather or other activities taking less time than expected.
>> 21st – Go up Jungfrau. I have been told by travel agents here in India that it can get pretty crowded there so possibly Glacier 3000 or Mt. Titlis could be a better idea.
You are looking at 3.5 to 4 hours travel each way for Glacier 3000 or Titlis.
Don't let the Jungfraujoch crowds put you off! Anyway, May is not high season, though may well be busy. Reserve seats between Kleine Scheidegg and the Jungfraujoch if you are worried about getting a seat on the train, but I doubt it would be necessary.
Personally, I wouldn't wait this long to go up to the Jungfraujoch. I would go up on the very first day when it is clear on top. It may turn out to be the only clear day during your visit - you never can tell!
>> 23rd – Golden Pass line to Montreaux (reach there by 1220PM), spend some time there and return via Brig to Interlaken (via Goppenstien and Kandesteg).
Going to Montreux via the Golden Pass route will take around 4 hours, and returning via Brig and Kandersteg will take 4 to 4.5 hours. Even going back by the fastest route will take 3 to 3.5 hours: so, 7.5 to 8.5 hours on trains for the day. Besides that, the first hour and a half of your proposed return route (the sector Montreux-Martigny-Brig) is pleasant, but nothing special for Switzerland.
>> Wanted to have one scenic train journey.
If you have travelled between Grindelwald and Luzern, you will already have done one sector of the Golden Pass scenic route. Going up to the Jungfraujoch, especially if you go up from Grindelwald and down via Wengen and Lauterbrunnen, you would be seeing one of the most stunning views in Switzerland.
>> I also need to include a visit to chocolate making and/or cheese making for kids.
You might find the chocolate factory at Broc and the cheese factory at Gruyères are too far away for a day trip (over 3 hours each way). What about taking your children to the Schuh Chocolate Show in Interlaken, which is on at 5pm daily?
>> 24th – Yet to plan, desire list – Glacier 3000 / Lucerne / ?
may be do Titlis along with visit to Lucerne – but on second thoughts, combining Titlis with Lucerne visit will become too tight!
As I mentioned before, you are looking at 3.5 to 4 hours travel each way for Glacier 3000 or Titlis.
Perhaps consider a PostBus trip from Grindelwald over the Grosse Scheidegg to Meiringen, and return by train. If you time it right, you could also incorporate a cruise on Lake Brienz.
The PostBus ride is an exhilarating ride through dramatic scenery. You could stop off at Grosse Scheidegg or Schwarzwaldalp along the way for lunch - but need to check the bus timetables to make it work. This route starts operating again on 20 May, after having ceased for the winter.