Summer trip Bavaria and Austria with teens

You probably have time for what you have planned if you push it hard. "Reasonable" might mean any number of things. One thing that seems off is June 29. That's the day one or more of you will likely be jet-lagged, and it is unwise IMO to have a plan that forces you into doing a long drive that same day. I am no proponent of visiting Dachau, with the exception that Holocaust deniers should be required to go there... but if you don't mind slighting your time in Munich and are keeping it on the agenda, you could perhaps do that along with Munich on June 29 and 30 instead of at the end of your trip. Use public transport for your Munich/Dachau stay, then pick up your car on the morning of July 1 for the trip to Garmisch.

Golling is a great little spot. Maybe it's just the fact that Rick's materials don't cover the area all that well... but one of the reasons we chose to stay there, besides the nice apartment and the scenery, is that Golling is a stone's throw from a couple of major attractions: Hohenwerfen Castle and falconry show, and the Eisriesenwelt, which lays claim to being the world's largest ice cave. Werfen is the town to head to for these experiences, as well as for the Sound of Music Trail, a pleasant hike that takes you to the mountain meadow from the film. Hohenwerfen, unlike Neuschwanstein, is a REAL castle - a true medieval fortress that has remained intact for centuries. (Construction on N'stein finished up just before the dawn of the 20th century. It's a modern royal palace by comparison - with a fake castle exterior.)

When you return to Germany, you can bypass Munich and stay in nearby Freising, just a couple of miles from the airport, which has easy bus/train access to the MUC airport terminal. Lovely town for a final day or half day, things to do, and the Weihenstephaner Brewery:

https://www.tripadvisor.com/Tourism-g198549-Freising_Upper_Bavaria_Bavaria-Vacations.html

By staying in Freising on July 8, you will be only a few minutes from MUC vs. 40 or so from central Munich.

And since the castles you hoped to see are in short supply, you might want to make a short detour on your final drive to Freising for Burghausen Castle, on the German side of the Austrian border not far north of Salzburg. The page below includes the Burg and other sights in the handsome town of Burghausen.

https://www.tripadvisor.com/Attractions-g198433-Activities-oa0-Burghausen_Upper_Bavaria_Bavaria.html

Two fun things we did in Munich that your teens would like:

Visit the BMW showroom and museum and look at all the cars

https://www.bmw-welt.com/de/index.html

and then walk over to Olympic park and look around and see what activities interest your teens.

https://www.muenchen.de/en/sights/attractions/olympic-park

A segway tour of Munich- we enjoyed the adventure and saw a lot in a short time.

https://www.fattiretours.com/munich/segway-tours/

the rowboats in the Englishgarten and drink a beer at the Chinese tower in the Englishgarten
While there, see the surfers on the river Isar

https://www.englischer-garten-muenchen-infos.de/en/#google_vignette

In Garmisch, be flexible with visiting the Zugspitze. If the weather is clear at the top on July 1, then go to the top of the Zugspitze on that day and then the castles on the next day. You don't know what the weather will be like at the top of the Zugspitse on July 2.
However getting advance tickets for Neuschwanstein boxes you into a set time to see it.

Also fun near the castles is the Tegelbergbahn luge/toboggan rides.

https://www.tegelbergbahn.de/en/summer/activities/summer-toboggan-run

Also in Munich, while its touristy, visit the Hofbrauhaus and have a beer there- if checking off bucket list items is one of your goals.

I did the Kobensattel (alpine slide) in Oberammergau, not too far from Garmisch. Very fun. Would recommend Ammergauer Maxbräu nearby for a meal as well.

Treetop Trail just south of Fussen is fun, not very long and you drive right past it on your way to Highline 179. For lunch, I'd recommend Schwangau Castle Brewery just east of Fussen. Great beer and views of castle from beer garden.

BMW Welt and Museum in Munich. My teenagers enjoyed welt more than museum.

Another quick and cheap activity in Munich is climing the 300 tower steps of Alter Peter.

Russ, thank you for your very detailed response. Actually thinking about taking away a day from Garmisch and adding it to Golling after your suggestions.

Derek, the Segway tour looks great. Definitely adding that to our itinerary! Hofbrauhaus is also on the must see.

Nixit 71, will do the 300 steps of the church in Munich. Also, love a good brewery and that one in Schwangau looks perfect.

Another question about car rental. We will have 10 people. Are there any 10 passenger van rentals? or is doing two vehicles the way to go? Thanks!

You have an ambitious itinerary.
I like Munich and think it deserves more than an afternoon. The Welt is a technically amazing building. Across the way we played minigolf in the Olympic park but you can also swim, possibly see a concert, ice-skate.
The Deutsches Museum was my sons' favorite stop in Munich but they also enjoyed- with audio tours they could go at their own pace- the Neue more than the Alte Pinakothek art museums- worth seeing.
July 1- "castles" undefined. We did the three castles in one day including Linderhof - my favorite of the 3 and had time for a few rodelbahn runs.
Dachau is not how I would spend a last morning in Germany, IMHO, it's a punch in the gut. Hope there is something that afternoon to erase the chill.
The Documentation Museum explains more about the Reich, also worth seeing.

with 10 full sized people (teens get big quickly) and luggage for 10 people it sounds more like 3 cars than 2.