3 teenagers in Switzerland for only 2 days!

Coming from Venice by train, but where and by what method of transport are you going afterwards?
2 days? how many nights is that? The train from Venice will take most of the day, so your arrival day is a wash. Depending on your departure you might not get any time on your departure day. So I hope your 2 days is 3 nights, i.e. not counting arrival or departure day.

You can do one-way (downhill) bike hires in Switzerland. On the flat bike rides and the Alps are a contradiction.

The Berner Oberland is a good idea (Mürren, Laterbrünnen. Wengen. Grindelwald etc.), but given your time and transport constraints, I would also consider Luzern.
Venice to Luzern by train: 6 hours 21 minutes.
Venice to Lauterbrunnen by train: 6h35
(train times from the Swiss Railways site: https://www.sbb.ch/en )

Luzern is a town, with a nice old town and town walls. The Berner Oberland is smaller places.

Luzern panorama: http://tour.luzern.com/360/en/
Luzern gives you a lake to take boat trips on. Luzern has 3 mountains you can go up: Pilatus, Rugi and Titlis. Titlis is the largest and has snow on top even in summer. Website: https://titlis.ch/en
Titlis has scooter bike hire, one-way downhill: https://titlis.ch/en/activity/detail/Scooter_bike/4485/60762

The Berner Oberland villages are up in the mountains.
See: https://muerren.swiss/en/summer/
https://grindelwald.swiss/en/summer/
https://lauterbrunnen.swiss/en/summer/
https://wengen.swiss/en/summer/

Your choice, depending on what sort of experience you want.

Whether this is practical at all depends on where you will need to be after Switzerland.

You could get to the Dolomites somewhat faster than to the Bernese Oberland, and without paying Swiss rail fares.

Lucerne is a decent option. Lots of teens enjoy the mirror maze in the Glacier Garden right next to the Dying Lion Monument.

However, if you want to see the Berner Oberland south of there, I'd recommend staying in Lauterbrunnen.
You say 2 days, but even with a day and a half you could do this:
Stay in Lauterbrunnen and rent bikes there. The only trail I'd recommend for bikes is riding south down the Lauterbrunnen valley to Trummelbach Falls, well worth seeing. That is the ONLY flat trail in the area and very well groomed with gravel.
For other trails, I do NOT recommend a bike, even though you'll see Rick Steves do it in one of his videos.
Why? Because a) you don't want to spend your time looking DOWN at the trail (for roots, stones, curves, etc.) when you could be looking at the magnificent scenery instead, and b) if you take pics you'll be riding for 5 seconds, stopping to take a picture, 10 sec. ride, stop again for a pic, etc. Going leisurely down these trails is a Plus!
In 2 days, you could
1. ride or walk down the Laut. valley to Trummelbach Falls.
2. Take the train to Wengen, cable car to Mannlichen, then walk from Mannlichen to Kleine Scheidegg, then train return. This is THE most panoramic trail in the area and is a must on a clear day. Walk is about 1.5 hrs.
3. Take the cable car up to Grutschalp and take the trail that parallels the train line to Murren and take train back or cable car down to Stechelberg and walk north up Laut. valley back to Laut.. About 2 hours one way, Grutschalp to Murren. Halfway to Murren is Winteregg where there is a cheese-making building just up the hill. Look in thru the windows.

What about the Schiltshorn? is it worth doing and eating at the revolving restaurant? or Are the above suggestions a better way to experience the Alps? How long is the train ride from Murren back to Lauterbrunnen?

The Schilthorn is accessible via Murren - do not go there for the restaurant. You go there for the views and perhaps hiking...but definitely not the food.

Care to answer Chris's question about your next destination after the Berner Oberland? Helps people formulate useful answers for you.

Dear Shoe from Grand Rapids: Thanks so much for this detailed information!! If you only had time for either #2 or #3. which would be better? (don't think we have time for both.)

Theoretically, with an early start, you could do all 3 in one day, since #3 includes #1, only walking the opposite way. (You can also take the yellow Postbus to and from Laut. to Trummelbach Falls that goes about every half hour to save time.)
However, to answer your question: definitely #2, espec. on a clear day. I consider this the best (sightseeing) trail in the world--seriously! Google image "Mannlichen" to see the start of it.

My two teens and I only had a few days last summer and I chose the Lauterbrunnen valley as The Swiss Experience--no regrets as far as how we spent our time! We did the Via Ferrata, from Murren to Gimmelwald and it was a peak experience, if you're up for that sort of thing! We were going to splurge on a guide, but learned that we needed to be a group of four to hire one. Turns out, you can rent the climbing harness, helmet and gloves from a sports shop near the start in Murren and return them to the lift in Gimmelwald. It was beyond scary, thrilling, and WAAAYYY out of my comfort zone but I did it--the kids (17 and 18) loved it and it was a great bonding experience--they had to talk me through a place or two which was a nice role reversal.

With our remaining time, we trained/hiked to Kleine Scheidegg and spent one night in a berg hotel on the mountain, which was also magical. There were a number of people on the trail with electric bikes which were available to rent. Have fun!

https://blog.ricksteves.com/blog/via-ferrata-—-scared-silly-on-the-iron-cableway-from-murren-to-gimmelwald/

Hi Aimee, Just re-read Shoe's list--we did both #2 and #3 last summer and I would vote #2. (Though #3 paired with the Via Ferrata was pretty cool.)

Since the original poster said, "Nothing crazy for this 52yo Mom", then Via Ferrata would NOT be for her. The teens might go for it though. Rick Steves did it and was scared stiff and said he had trouble sleeping that night. You may be able to find the video.
For those of you not familiar with it, Via Ferrata is a walk across a cliff face near Murren where you hang on and lock on to cables to prevent falling to your death. It may be safe, but will scare you half to death.

Rick Steves talks about his experience on the Via Ferrata here, at the 22min mark:

https://www.youtube.com/watch?v=QH5rjywpRSs