Too many thing to see in 3 days, need advise

Hi tiamaria, and welcome to the forum! It's great that you get to visit Switzerland once again. Your itinerary doesn't look too ambitious. The timetable allows you to find out about traveling times.

As for rail passes: in fact, a Swiss Half Fare Card would be a bit cheaper than the Swiss Card in your case. In all, this may be the cheapest solution. However, if the idea of free traveling without the need to buy separate tickets appeals to you, you could consider a 3 day Swiss Saver Flexi Pass or a 4 day Swiss Saver Pass, covering all your travel during your stay (except for mountain transportation such as the cable car from Engelberg to Titlis: this one's reduced by 50% instead of for free). I'm not quite sure whether your stay will last 2 nights/3 days or 3 nights/4 days, that's why I mention both the 3 and 4 day variant. If the 15 and 4 years old are children of one of the adults, you can obtain free STS Family Card along with your Swiss Half Fare Card or Swiss Saver (Flexi) Pass, allowing them to travel along for free with their parent(s).

Your rail pass, whether it's the Swiss Half Fare Card or the Swiss (Flexi) Pass, is valid up to Buchs. From there on, you have to buy a regular ticket to Inssbruck/Salzburg.

Weather is Switzerland is very unpredictable. April can still be cold and wet, but there have been many years with great, sunny spring weather. Generally, nature in the lower areas of the country starts to bloom and blossom by April, whereas higher regions may still look like it's winter. Just be prepared for all kinds of weather and arrange for a back-up plan, such as your trip to Bern. It's not the best time yet for alpine flowers.

Thanks for sharing your good experiences tiamaria! The regular fares can be found in the timetable, as explained here.