Question- We (husband, myself and son) have 1st class Rail Pass in Germany and a 2nd class in Switzerland. We will be traveling from Munich to Interlaken so how does one go about doing that? Returning we are going from Zermatt to Frankfurt... Suggestions?

If you come from Baden-Wuerttemberg, you may spend a few hours in the interesting border towns (Basel with medieval center, cathedral, fine museums, Picasso exhibition, etc; resp Schaffhausen with medieval center, castle, Rhine Falls; Konstanz, not far from the splendid Mainau Island, medieval Meersburg and the Unteruhldingen Lake dwellings) anyway.

Will both railpasses still be valid (date-wise) for both
parts of this trip? If so, no problem.
You know of course that these are mighty long travel days if you choose not to break them up...ie:
Muenchen--> Interlaken West is 6 to 7 hours and involves 1 -4 train changes.
Zermatt ---> Frankfurt Flughafen (airport, i'm presuming) is 1/2 hours and 3 train changes...

You can check your train date train itineraries at www.bahn.com

Sorry--Zermatt to Frankfurt airport is 6 and 1/2 hours!

They will be, I just want to make sure you can walk from 1st class to 2nd class and vice versa so as to not get in trouble... We are staying in Bacharach the last evening so Zermatt technically to Bacharach. Yes I know, two long jaunts...

Yes when the German train hits Switzerland just move into 2nd class - often in an adjacent carriage. Actually your train will go thru a touch of Austria around Bregenz where neither pass will be valuable so buy that supplemental ticket in Munich before getting on the train - the conductor will sell you the Austrian portion ticket on the train maybe - not sure - but may have some penalty fare in it for not having a ticket. Ask about this at the Munich train station.

When leaving Switzerland in 2nd class you can then stay in those seats even if you have a first-class pass or of course to realize the immense benefits IME of first class on German trains then move to first class at your leisure.

for lots of info on German and Swiss trains I always spotlight these IMO fantastic sources - www.ricksteves.com; www.seat61.com and www.budgeteuropetravel.com.

And when coming into Switzerland from Austria you do not have to get off the train to activate your pass but the conductor is required to do it on the train but only if you are on a train that runs directly thru the border - this is so you need not have to get off that through train to activate the pass and miss that train.
Normally passes must be activated at a train-station ticket window - showing your passports, etc - but the caveat for coming into a country on a train the conductor then does it on the train - it should say this in the railpass use conditions.

Thanks so much PalenQ. You provided me with invaluable information in planning this whole trip. We are staying in Interlaken for three nights because of you!

Well don't blame Interlaken on me! Just joking as some Fodorites don't agree with my take on Interlaken being nice - thanks for the thanks. Report back about Interlaken!

going back you probably are best going via Basel where there is nearly always a change of trains anyway.

Zermatt - Bacharach: 7 3/4 hrs ride, trains about every hour from 7.39 until 14.39. Change at Visp, Bern, Basel, Mannheim and Mainz

I note on some links thaking 7 3/4 hrs there are direct trains between Bern and Freibourg in the Black Forest area - thus potentially you could be on a train where you'd have to switch cars en route - but it seems most links require a change of train at Basel so no cross-border travel on most on trains that directly go thru the frontier.

Great. It is ok to get up and move then while the train is moving too. Thank you!

Great. It is ok to get up and move then while the train is moving too>

Of course - as soon as it leaves Basel SBB and crosses the Rhine and arrives at Basel's DB (Basel Bad Bf) or German train station!