Berner Oberland 5 Days with Teens

It might help to add departure and arrival points--is it a full five days, or will you have to move closer to an airport on last night?
I'd say make them tough it out (ha ha, not like Switzerland is a punishment)--after Paris a little quiet won't hurt anyone, and the convenience of being able to just set out on a path is invaluable. I was in Murren in late October and so it was pleasantly calm, but I bet in July there will be kids running around in evenings. It may very well be much more exciting to them than you anticipate?
With accommodations being what they are in Switzerland, I would dive in and see what's in your budget and see how that sways things.

Staying in Murren will allow your kids to see others their age mountain biking, paragliding, hiking and the like. The area has youth hostel kids and other groups of teenagers on their gap year/senior high school trip from around the world to meet and have fun getting to know. To me it is a perfect place to stay with teenagers. Plus, there are tons of great hikes right outside your door. There are Airbnb's in Murren, not many, just check the map to make sure it's Murren and not across the valley in Weigen or other. J

Yes, with as beautiful as the area is they will be in awe. Updated post to include travel dates - seems like Paris to Switzerland is a scenic train ride and hopefully could get to one of the towns by late afternoon. Getting to Florence from BO may be more of a challenge.

I'd go for Murren or Wengen. We are big Wengen fans. Not as busy as Grindlewald or quiet as Murren, plus it is right in the middle of everything. Part of the fun is using the different types of transport, but it can add up! consider North Face trail out of Murren plus trip up to Jungfrau if you can afford it. Our Middle and High Schoolers all loved this trip. You can easily fill 5 days there and rain days can be spent in Interlochen or Ballenburg which we spent the whole day at during a rainy stretch. Enjoy!