Please review my itinerary

Just addressing the notation on Day 1 about buying the €9 tickets: You can buy them ahead of time online - that way you don't have to waste time in Munich buying train tickets. Just go to the Deutsche Bahn website, scroll down to the €9 ticket info, click "Choose Now", then pick your month and book the ticket.

You will need to set up an account but it's very easy and they will email the ticket to you. If you download the DB Navigator app, the tickets will be stored in there, and all you have to do is show the conductor the QR code.

It's a bit aggressive a schedule, buy that works for some people. In Budapest, and most of your other stops, you will benefit from a guide to get the most out of your time. I can help with Budapest guide and maybe some ideas on how to use the time.

James E: Thank you..I realize it is bit aggressive. I got a flight ticket with good fare for the 17 day trip. To make use of the high speed train corridor between Munich and Vienna/Budapest, I come up with this plan.

Any tips/suggestions on guide service at Budapest or other location will help me.

That is an aggressive schedule, perhaps too many day trips? I assume you are all morning folks and the young people get up and out early? Also, no flexibility for unfavorable weather.

Would everyone be upset to skip Fussen? You will have beautiful mountain and lake scenery in Hallstatt and Berchtesgaden, and it's much less commercial than Fussen.

I'd suggest staying in the old town in Salzburg, in the pedestrian-only zone. I was just there in April, and it's so nice to go back to the hotel midday and take a little break. Also, family members can go off on their own, perhaps do a little shopping, or return to an interesting site.
Don't forget Salzburg's Augustine's Beer Garden, a 30 minute walk across the hill from the Fortress!

Either way, have a great family trip!

For the Budapest guide either Andrew Illes http://www.guideinbudapest.freeweb.hu/ or Ekateryna Prokhochuk https://community.ricksteves.com/travel-forum/general-europe/excellent-new-guide-in-budapest-with-a-wonderful-twist#bottom

I think it sounds good. As a solo traveler in my 30s, I’ve spent similar amounts of time in all those places except Budapest. And I haven’t seen the area around Tegelberg. I went to Ludwig’s castles as a day trip from Munich, and it took all my day’s energy to do that. If you choose to stay in Munich on night 2, it might be over ambitious to go to Tegelberg. But by moving to Fuessen, you’ll have to find somewhere to stow luggage in the morning before the castles. But I think the advantage of a Fuessen stay is getting to the castles before the tourist throngs from Munich, so you’d want to stay the night there before you visit the castles?

I wasn't being critical of the aggressive nature of the schedule. I've done it a few times myself.

You are going to be amazed at the "high speed rail service" Vienna to Budapest!!! I think the train hits 65 mph on the straight stretches which is how its able to cross 150 miles in an amazing 2.5 hours.