Do we need a train pass if we plan to do a lot of hiking in Juanfrau region?

You will have to do the math yourself, but certainly the Half Fare Card will save some money. A 5-day Jungfrau Travel Pass will cost you 210 CHF with the Half Fare Card. See if there are any savings, or perhaps only a convenience factor.

Based on your plans, I’m assuming you’re a very experienced and skilled hiker. Some of these hikes seem like you’re just hiking to save money, as you’re hiking routes that transportation would get you to and missing out on the hiking that gives you the best views. For example, hiking from Wilderswil to Schynige Platte is not an exciting hike at all. It offers very little views, whereas you could take the cog train up to Schynige Platte and then do the very beautiful hike from Schynige Platte to First. Same goes for hiking from Wilderswil to Grindelwald to First. That’s not a scenic hike, but the above combining Schynige Platte to First is very scenic. My husband & I spend our summers living in Murren to hike and none of your plans are ones I'd recommend.

Is your purpose just to save money or have you actually researched what’s involved with these hikes?

Hiking from Gimmelwald to Schilthorn and back is a massive hike that takes around 10 hours and involves some really rough terrain with over 5,000 ft of elevation gain and 5,000+ ft back down. I can’t see any scenario where it’s of value to hike both up and down and doing it from Gimmelwald instead of Murren makes it even harder.

Hiking up to Mannlichen from Wengen is around 3,500 ft up and very steep with views of switchbacks the whole way.

Wilderswil to Schynige Platte is almost 5,000 ft up and a lot of woods.

Wilderswil to First is going to be 4,000 ft up and the route from Wilderswil to Grindelwald is not interesting.

The Harder Grat from Harder Kulm is an extremely dangerous hike that people die on. It’s over 3,000 ft of gain but involves some very dangerous ridges. Unless you’re an extreme hiker, I do not recommend it. There are other alternatives that are just as beautiful with less death as a legitimate concern.

Thank you so much for taking the time to share your insights. My husband and I do love hiking and have done quite a bit over the years, but you're absolutely right — I planned these routes mostly by studying maps and trail connections, without truly understanding the terrain or the quality of the views. Your feedback is incredibly helpful, and I really appreciate the detail you provided.

It definitely wasn’t about saving money — we’re more interested in experiencing the beauty of the region through hiking, and I now realize that some of the routes I picked may not offer the best payoff in terms of scenery or effort. I’m especially grateful for your notes on elevation gain and trail difficulty — those are things I hadn’t fully grasped.

We’ll be staying in Wilderswil for a few nights, so if you have any favorite hikes — especially ones with stunning views, interesting terrain, or good wildlife/birding opportunities — I’d love to hear your recommendations. Thanks again for helping us make the most of our time in this incredible area!

OP - do you use Caltopo, Gaia, All Trails or some other software for mapping and planning your hikes?

I ask since I make sure that I know what the elevation gain and often, more importantly, what the descent is going to entail. I just returned from doing about half the Alta Via 2 (Gran Paradiso area) and we dropped a number of segments when the elev gain was well over 5,000 ft and some where the descent was either over 6,000 and in one case almost 7,000 ft. We decided it was better to save our knees for future hikes than to attempt a couple of the descents.

Get the SwissTopo app. This app shows you a topographic map of Switzerland, and shows where all the hiking paths are. You can there plan a trip, and you will be shown distance, a height profile of your walk, and time estimates.

Your Day 1 !!!! I would love to meet the person who walks from Murren to the Schilthorn and back in a day!!! Seriously, you've set yourself an impossible task there, I'm afraid.

What seems more doable is something like what we did. From Murren (or Gimmelwald), take the cable car up to Schilthorn, and then down to Birg. From Birg there is an amazing hike down to Murren (or Gimmelwald, or Stechelberg, or as far as you want to go), including alpine lakes, 360 views, going behind waterfalls, an alpine chalet / rest spot/ restaurant, and an amazing experience. Just this downhill hike took us 3-4 hours if I recall (count on 6-8 going up this mountain). If you're interested, DM me and I can share the exact route we took.

Sounds like you will be rethinking your routes.
We were just in Lauterbrunnen for 3 days. We didn't get to hike everything we had planned due to weather. Swissfamilyfun.com was a great resource for planning our hikes.
She has very detailed posts and videos of many hikes. They all include elevation gain/loss, Approximate cost for lifts, extensions...she also has a great round up of best hikes that is a good starting point.