As Swandav suggested would like a stop over , just to explore quickly. How ever what will happen to seat reservations.

Should I get the reservations only up to Gstaad and then take next local to Montreux>

Well the best scenery is after Gstaad - righ at Gstaad area and to Montreux - so how about taking a local - no reservations required on those trains and book the GP train from Gstaad to Montreux?.

Seat reservation in Golden Pass Panoramic and Classic trains is not compulsory, but recommended. In the last weeks (narcissus flowering season), I crossed a lot of half empty Golden Pass trains.

One novel things my GP train had was swivel seats so you can turn as the scenery dictates - this was in first class but perhaps on 2nd class too but only in certain cars? A group of beer-bellied Germans were having perhaps too much fun swiveling in their chairs, steins in hand!

FYI - Trenitalia is finally loading the Venice/Milan trains for your dates. The trains you want appear now, but can't be purchased yet. All trains are currently listed as "solution with one or more segments not sellable" even though they are one segment without changes. Even trains in July are listed as not sellable as are trains this week. Hopefully they will have this fixed in the next few hours. You should have the choice of these two trains unless you want to leave earlier:

Venezia S. Lucia
07:50 Milano Centrale
10:25 02:35
FRECCIABIANCA
9708
Travel solution with one or more segments not sellable

Ve. Mestre
08:32 Milano Centrale
10:55 02:23
FRECCIABIANCA
9710
Travel solution with one or more segments not sellable

The second one departs Mestre. There are about 4 trains per hour between Venice SL and Venice Mestre with travel time about 10 minutes if you need to choose the Mestre train.

Kybourbon - Many Thanks.

Managed to pick up tickets on 07:50 Train.
No discount tickets(9EUR). However applied "BIMBI GRATIS" - Excellent suggestion. All in 113EUR.

only one thing left now - Place to stay in Lucerne for 2 days

From what I gather to get those 9 euro tickets you must pretty much nab them when they come on the system and in this case even then they apparently were quickly sold out and maybe some popular trains do not even offer them?

The 9€ fare is available the that route, very same time on the next day and again on the 8:25 departure.

Venezia S. Lucia
07:50 Milano Centrale
10:25 02:35
FRECCIABIANCA
9708
Price starting from 9. 00 €

There are lots of 9€ fares available. It may be harder to find them on a Monday morning which is what the OP needed as you have business people traveling. There were 9€ fares for five AV trains later that day. There were still 19€ discount tickets for the OP's train (regular fare is 37.50€), but the OP saved a few euro over that by booking the Bimbi Gratis discount (kids travel free) instead of the 19€ economy discount tickets (can't combine multiple discounts).

>>>and maybe some popular trains do not even offer them<<<

I see discounts offered on most fast trains, but the 9€ not on every route. Some routes, the cheapest fare offered is 19€. Long routes might have 29€ as the cheapest, but often regular fare on a route like that is 75-100€. It's usually very easy to find them on IC trains.

I got 2 for 19€ and another 2 for 37.50€ and 3 kids free of cost. I call it a good discount and no complains.

I had to take the morning train on Monday to get connection from Milan to SPIEZ at 11.25. No choice here since I have a confirmed Wengen for Monday.

Any suggestions on - Place to stay in Lucerne for 2 days.