Train transfer times - 7/ 8 minutes enough?

No worries, Swiss trains run like a.......Swiss watch.

At Bern, you will use the overhead bridge, up the steps, cross to the next platform, then down the steps to the new track. Just be ready by the door with your luggage when the train stops so you can exit the train quickly. Should take no more than 3 minutes.

At Interlaken Ost, the train will terminate there. You exit and go down the stairs to the under-track passageway, walk about 50 ft, then up the stairs to the new track. The train to Lauterbrunnen splits half way to Lauterbrunnen with the other half going to Grindelwald. Make sure you board carriages marked "Lauterbrunnen". The train will be waiting for you. Should take you about 5 minutes.

If you miss a connection due to to a late arriving train, take your Super Saver ticket to the ticket window and they will endorse it for the next train.

That's normal. Plenty of time. If you look on the SBB website you can see the platform numbers. It may even be just the opposite side of the same platform, no stairs.

If you miss your train because the previous train was late, then you are allowed to use a later train.
Note the train from Interlaken to Lauterbrunnen divides. It is a Y-shaped route, half the train goes to Lauterbrunnen, and the other half to Grindelwald. the coaches are labelled.

Totally doable - I've done connections in Bern many, many times with connecting times even shorter than that. Depending on where your car is in the station, you either have an overpass or an underpass to move between tracks. Download the SBB app - it'll show the track (Gleis) of your connecting train in real time. You can also listen for announcements both as you pull into the staton on the train intercom as well as the platform when you allight - they'll tell you the track to go to. Announcements are generally in German, French and English.

Thanks so much for all the input, our tickets is booked!!

I’d suggest taking screen shots the night before of your route. This will show your arrival and departure platforms. Especially good if you aren’t using cellular service.