Road trip in the Germany, Austria and possibly Switzerland

I like to start in Munich and go east to Salzburg and Vienna. Respectively, they're good for 4/2/4 days' time each.
Then we often dip into the Alps (south of Munich) to see the incredible scenery--Innsbruck area for 2-3 days. Depending on time, you can also go on south to Venice for 2-3 days.
Many will go northwest of Innsbruck into the Neuschwanstein/Fuessen area to see Crazy Ludwig's "castle."
I shop Hertz using my Gold Club and AutoEurope.com--and will take whichever's cheaper. With five travelers, you'll probably need to go a van. Westfalias are campers, and probably too expensive and difficult to find in rentals.
Depending on the time of the year you're going, you may can book rooms as you go if you're carrying a way to get into the internet. It's usually best if you have your room at the first stop and the last stop reserved, however. Figure out what cities you want to go to, and chime back on here asking if anyone knows of any good B&B's or places to stay. Traveling with 5 is sometimes a little more complicated.

Vince, for transit times and an approximation of fuel and road tax costs please visit ViaMichein.com. You did not state if you were traveling open jaw or returning to your start point. Please be aware of the very high drop charge if you rent in one country and drop off in another. Driving in Germany is easy and pretty much hassle free. Familiarize yourself with the road signs and what they mean. Also, parking signs. You could land in Munich and plan your itinerary from there. There are many interesting cities to see and spend some time in. What is it that you and your family like to do?

Thanks so much! This gives me a good place to start. Should we even attempt to make some routes in trains? Or just go ahead and have a car? I prefer that we don't have to book everything in advance to allow some flexibility. Just concern if booking is as easy and available if we can be flexible.

1) Are the hotel room offers 2 double like in the States? Or do we must book 2 rooms? Our youngest share bed with us.

2) How about flying in and out? Same airport to do a circular type itinerary or start at one and end at a different one?

3) International license required? Or the US license will suffice

Thanks so much for all your advice.

After much searching, since it's the five of us, it's the most economical to fly in and out of Frankfurt. We will have 17 days total, given 1st and last day are in-flight. So 15 days on land. What would be your ideal itinerary?

We don't know your preferences, but a nice circular itinerary would include: the Middle Rhine valley, the Black Forest and Alsace, Lake Constance, the alpine region of adjacent Austria (Vorarlberg and Tyrol) including Innsbruck and possibly a detour into South Tyrol / Trentino (dolomites), Salzburg, Munich, Franconia (Nuremberg, Bamberg, Würzburg) - Frankfurt.

To get an overview search at Google maps or Viamichelin for these stops: Bacharach - Colmar / Freiburg - Triberg - Lindau - St. Anton am Arlberg - Innsbruck - - Ortisei - Garmisch - Berchtsgaden / Salzburg - Munich - Nuremberg - Bamberg - Würzburg - Mainz (or some other place near the airport for the last night).

For Austria an international driving license is mandatory.

For your question about a room accommodating that number of people, you may want to have a look at the replies in this thread. (Hope I get this right with the link.)

Though you may be more lucky with only two adults. What ages are your children?