Advice on 7 day itinerary please!

Lots of good stuff in there, but here are some things to reconsider.

Day 3: You do NOT want to hike from Kleine Scheidegg down to Wengen. My son (14 at the time) and I tried it and the constant down slope began to hurt our shins a LOT after 45 minutes. There are much better hikes (click on my name to find a link to them.)

Day 4: You could walk from Grutschalp to Murren (or half way to Winteregg). It's a nice hike (2 hrs) where the snow-capped mountains are almost constantly in view.

Day 5: I believe the cable car from Mannlichen down to Grindelwald is being reconstructed this summer, and not available. But that's ok, because the better route is to take the Mannlichen to Kleine Scheidegg trail (1.5 hrs, and my favorite trail in the area), then take the train down to Grindelwald.

I suggest you compare the validity of the 8-day Berner Oberland Pass ( cost 350 CHF) with the 8-day Swiss Pass (418 CHF):

https://www.regionalpass-berneroberland.ch/assets/pass-und-infos/geltungsbereich/Geltungsbereich-2019.pdf

https://www.sbb.ch/content/dam/sbb/de/infotexte/uebersichtskarte-sts.pdf.sbbdownload.pdf

The Swiss Pass will fully cover boats on "Lake Lucerne", the train up to Schynige Platte, and the cablecar up the Schilthorn, and will give you 50% off the Pilatus route, the cablecar up to Männlichen, the gondola down to Grindelwald, and the First gondola. And will fully cover your train travel between Zurich and Wengen.

The Berner Oberland Pass will cover your train travel from Luzern to Wengen and Wengen toward Zurich as far as Luzern or Bern. It will also cover (fully) the Männlichen cablecar and First Gondola, and the train up to Schynige Platte. The map does not show the gondola down to Grindelwald from Männlichen; they show a bus route instead, but I wonder if that just reflects a failure to update the map ( the gondola between Männlichen and Grindelwald was just rebuilt and re-opened).

The BO Pass will not help at all with boats on Lake Lucerne or the Pilatus trip, and provides only a 50% discount on the Schilthorn cablecar above Mürren.

It will take some number-crunching to figure out which is best for you. And you should also consider a Half Fare Card (120 CHF). which will give you 50% off everything, but no free travel.

The Berner Oberland Pass will

Thank you both very much for your feedback, it's much appreciated. Could you suggest the best site to crunch all the numbers? I couldn't find the one site that you can calculate trains, cable cars, gondolas etc. Or is it just a matter of calculating on different sites? Leaning to the half price Swiss pass at the moment but as your said I would like to calculate our entire trip from budget perspective. Thanks again.

Can I just ask - as there is so many opinions on the internet, should we pre-purchase our tickets and seats from Kleine Scheidegg to Jungfraujoch as we'll be there in mid July - the busy season. In the case of weather being bad, we didn't want to go up but be locked into a date. Is it OK to purchase on the day? If weather is good we plan to go as early as possible - the first cable car up and that's easy as we will be based in Wengen. Thoughts?

Do not purchase any tickets in advance, you can buy them on the day, after having looked at the weather.
You can get prices (and train times) from the SBB (Swiss Federal Railways) website: https://www.sbb.ch/en/
Beware, the first price shown ("from") assumes you have a Half Price Card. Click on the price for other options. The Full price will generally be double the price with a Half Price Card.

I would definitely look at the weather before buying tickets to the Jungfraujoch, and going first thing is often the best strategy because summer afternoon clouds can build up at the mountain tops.
BTW, it is a train up to Kleine Scheidegg, not a cable car. If you take the cable car, you will be quite a hike to Kleine Scheidegg.

Here is a calculator you can use to calculate the optimal type of pass.
https://www.myswissalps.com/train/ticketspasses/practical/chooserailpass

If saving money is a top priority, the 30 day Half Fare Card wins 95% of the time. Passes have some intrinsic non-monetary value in that for regular trains, you do not have to stop and buy tickets, just get on the train and show the pass when the conductor comes by. Free museum admissions are a benefit, but not many people go to Switzerland to visit museums.

Thanks very much for your advice. On that note, do we need to pre-book anything then for our itinerary? My only concern was Jungfraujoch, which we'll monitor the weather, but everywhere else I am sure we don't need to pre-book.

You need to reserve hotels before you leave home, and your flights to and from Switzerland.
You do not need to pre-book any transport, in most cases it isn't even possible to do so. Treat transport like you would a lift (elevator) in a tall building. You make sure you go to the correct one going in the correct direction, wait until it arrives, get on and make sure you get off at the correct place. Nobody to interact with except the ticket inspector who checks your ticket on the train.

Luzern is lovely. You will be doing a lot of mountains in BO. I would skip Pilatus in Luzern and concentrate on the city if you are only going to be there a day, especially if there is not good visibility the one day you have to go there.

Thank you. As we'll be in Wengen for 4 days in mid-late July we are quite flexible and will wait for weather to be good to visit Jungfraujoch. My question is - is it too late to book the night before for a ticket from Kleine Scheidegg to Jungfraujoch and back for two? We aim to take the very first train up in the morning.

I saw you are able to reserve seats (at https://www.jungfrau.ch/shop/en/bergbahn/reservation/) but you can buy your train tickets separately to that? So I am a bit confused - should I reserve seats or just wait and see if weather is good? This is mid-July though so worried it'll be super crowded.

weather is critical.

Look at the screens and television channel when you get up. Don't try to go up Jungfrau from Luzern. In the 3 hours plus time up the mountain the weather can and likely will change.

Coming out of the tunnel at the top of the mountain into heavy cloud is a waste.

First train up is a good idea if the weather is good, and probably less crowded.

Yes, thank you Nigel. We are based in Wengen. So if we wake up early, and check the weather, and it looks good, then we can jump on the train to Kleine Scheidegg and buy our tickets to Jungfraujoch on the first train up? All without needing to pre-book or reserve a seat? (This is in middle of July).

Honestly, I would skip the Jungfraujoch. It is a minimum 4-hour time investment, dense with humanity, and expensive even with a rail pass discount. And it's only worth going up there if the weather is great.

Therein lies the paradox. If the weather is great then there is no better place to be than on a sunny alpine trail.

Unless I am tied into a certain schedule due to timed tickets, I rarely will have my itinerary set in such detail day by day. Weather is such an important factor, especially in Switzerland, in the enjoyment of many activities. What I do is make a list of the sights I want to see and determine fits in my time frame. Each day, I check the weather and start with one of the lengthy activities and fill in as the day progresses.

Yes that all makes sense, thank you. My question still - say the weather is good and we want to go up to Jungfrau from Wengen, is it still OK to buy tickets on the day for the train up to Jungfrau, in mid July, assuming we go early in the morning? I have read posts saying we should pre-book seats at least and it's still a bit confusing for me.