What passes should I buy for this itinerary and should I reserve any seats /buy tickers in advance for boat /cable car tickets ?

Arrive July 8 Zurich airport - train to Interlaken
July 8 - Interlaken
July 9 - do boat ride on lake and Waterfalls
July 10 go to Grindelwald
July 10 - First walk Grindelwald
July 11 - Jungfraujoch
July 12 Train to Zurich (Stop in Lucerne for a few hours) - July 13 depart Zurich airport

Does this sound okay for timeframe and worth getting Swiss Pass or Half Pass? We are mom and 17 year old son.

thanks for advice!

No need to reserve seats on trains, and no need to purchase tickets in advance. You'll want to see what the weather is like before purchasing tickets to the Jungfrau. I've not been up there in years, but we purchased on the same day.

A six day second class Swiss Travel Pass is 359 chf, an eight day pass is 389 chf. That gives free travel on your entire itinerary with the exception of the trip to the Jungfrau, which is only 25% reduction.

The Half Fare Card is 120 chf, and all transport on your itinerary would be at half fare.

You'll need to crunch the numbers to see which works best for you...or wait for neckervd, who might do it for you

The advantage of the Swiss travel pass is you just hop on a train without the need to buy a ticket (Jungfrau excepted). You'll need to purchase tickets for each journey with the Half Fare Card, but that's easy to do, especially if you have installed and registered on the SBB app.

Interlaken and Grindelwald are less than 40 (very scenic) minutes apart. You may wish to weigh up whether you prefer to stay in one place rather than move hotels. Also, suss out the best day to visit Jungfraujoch, depending on the weather. Schilthorn is another great alternative (different but also wonderful).

With your itinerary, as well as comparing passes/cards, you should also look into plain old point to point tickets. I don't know without checking which would be more affordable but it's easily worked out using sbb.ch/en.

I would pick one base in the Berner Oberland for your entire trip. Grindewald, Lauterbrunnen, Murren, and Wengen would all be good options, even for your exploring of the lakes around Interlaken (Thun and Brienz). The trains (and lift, in the case of Murren) will get you anywhere you want to go in this region in less than an hour; just think of it as commuting. I loved the convenience of the travel pass, but if money is an issue, you'll have to crunch the numbers to know whether the travel pass or the half fare discount is the better option. By having one base and being flexible, you can pick the best weather day for your trip to the Jungfraujoch.

ZRH - Interlaken is only 2 1/2 hrs by train, trains every 30 minutes, change at Berne.
Lucerne is much more scenic than Zurich. I would stay as lang as possible at Lucerne and go directly to a Zurich airport hotel in the evening (1 hr by train, trains every 30 min).
Rail Passes:
all depens on the mountain railway rides you plan to do.
You may check:
Swiss Travel Pass (almost no reduction to Jungfraujoch)
Swiss Half Fare Card
Bernese Oberalnd Pass https://www.regionalpass-berneroberland.ch/en/
Jungfrau Passes https://www.jungfrau.ch/en-gb/jungfrau-railways-passes/