Lake Thun & lake Brienz boat trip upgrading

We are getting the Swiss Half fare card & STS Family card.
We are planning to upgrade to 1st class on lake Thun boat BAT9 and lake Brienz Boat BAT67.
We are unsure how these boat look like, is it worth the upgrading?
Do my 3 children age 5,12 &13 travelling on STS Family card allow on upper deck (1st Class)?

Thank you.

Hello ccky1970,

Although not all boats are alike, you may get an idea of the possibilities here.
And yes, I would certainly advise to upgrade your travel documents to first class. Just go to the ticket counter, show them your passes and tell them what you want.
If you have a valid first class ticket, and your children have a STS family card and travel with you, they will be allowed in first class as well.

Thank you for the info! We will upgrade both the boat trip.