4 nights in Murren

I am not an expert on these passes, but if you have not been to Murren before, what I learned from my trip, there is that I didn’t know in advance which transportation we would be taking each day. We used the weather forecast and our list of hikes to decide what to do. So that made it very difficult to price out the options with different passes in advance. We chose to get the half price card and I never went back to do alternative math and find out if we could’ve done better, but it seemed to work out fine for us.

Unless you list your specific planned activities it's impossible to say. If you get the half fare card, get the free family pass with it so that your 14 year old travels 100% for free. You should have done that before purchasing your tickets from Basel to Interlaken and the Saver Day Pass though, because you likely bought uneccesary tickets for them and overpaid for those 2 days for everyone. It's really important in Switzerland to determine your full picture with passes before purchasing any tickets. Since you've already purchased some of your tickets the math may change and if you're doing mostly hiking/paragliding directly from Murren then you may not benefit from any passes at this point.