Garmisch and Innsbruck are on the same main rail line - about 2 hours to Innsbruck - so maybe stay in Garmisch then mosey on by train to Innsbruck - for Fussen and Mad Ludwig's castles take the train - about 2 hours and get a Bavarian Pass where up to five people can travel on regional trains all day as well as buses and trams ans S-bahns in Munich. Buy that pass at train stations - if you want to stay in Fussen you can take a train from there to Garmisch by taking a short bus ride thru the gap to Reutte, Austria, on a train line to Garmisch and Innsbruck.

For loads of great info on German and Austrian trains I always highlight these IMO superb sites - www.seat61.com; http://www.budgeteuropetravel.com/id9.html and www.ricksteves.com. And never worry about getting on those trains - never a problem if you just show up IME right before the train.

Garmisch would be a good base for all three IMO - check out the buses to Fussen from there or the train to Reutte and bus thru the gap to Fussen - Innsbruck is a short train trip and you can day trip easily into Munich. Could ski at Innsbruck and Garmisch both. Nice to base in one town and not have to relocated IMO.

I greatly appreciate your suggestions. A couple of additional questions...
Is it feasible to go Munich to Garmisch (to check into hotel) and on to the castles in one day?
Any specific ski areas that you would recommend - my son is a 22 year old very good skier -
Skies several times a week here in Utah.
Thank you very much.

Not an expert on skiing but I have been to Innsbruck's Olympic Skiing areas - I believe they are more widespread and challenging than anything in Garmisch.

One such ski area is just south of Innsbruck and reachable my a mountain tram from the city center.

Not sure how far Kitzbuhel is from Innsbruck but think it is not far and that, along with St Anton are some of the primo Alpine resorts.