There are 5 main legs to our trip: FRA Airport to St.Goar,
St.Goar to Rothenburg, Rothenburg to Munich, Munich to Berchtesgaden, Berchtesgaden to Munich Airport.
Day and side trips are: RT St.Goar to Koln, RT Munich to Fussen, RT Berchtesgaden to Salzburg, StGoar to Bacharach-Bacharach to Bingen, and other Rhine base trains/boats/feriies to get around.
After all my homework I'm still stuck. I was thinking 4Day Twin Germany Rail Pass at $199pp for the 4 most expensive tickets and then work with Lander and Bayern tickets for the rest. Any suggestions are a welcome.