I am trying to figure out the most economical way to get a group from Boppard, Germany to Colmar, France on a Sunday without a large number of train changes. I think one way would be to purchase the Lander tickets for Rheinland-Palatinate and Baden-Wurttemburg - these would get us from Boppard to Basel and then we could get a TER group fare from Basel to Colmar. Each Lander ticket would be 27 euros for 5 people, so the German part of the trip would be just a little over 10 euros per person. And we'd only have to change trains once in Germany. Does this make sense?
Nice in theory, but... The least number of train changes I see in Germany are three (Mainz, Karlsruhe, and Offenburg). With express trains you could probably do it with one change, but you cannot use Länder tickets on express trains. And, BTW, Rheinland-Pfalz- and Baden-Württemburg-Tickets are now €28 for up to 5 people.
I think the farthest you could get on one regional train from Boppard would be to Frankfurt Hbf.
And, one other thing. The Baden-Württemberg-Ticket is valid to Basel Bad Bhf, which is in Basel, Switzerland, but is technically a German station. I'm not sure you could get the SCNF group ticket there. You probably could at the SCNF Bahnhof, which is attached to the Swiss Bahnhof SBB. The Basel Bad Bhf is a short streetcar (~3.80CHF) or train ride to the SCNF/SBB Bahnhof, but that wouldn't be covered with the B-W-Ticket.
Update: It appears that a Baden-Württemberg-Ticket is valid on regional trains between the Basel Bad Bhf and the SBB Bahnhof. (German Rail passes, however, are only valid to Basel Bad).
If they are going on a Sunday, then they could use the "Happy Weekend Ticket" that covers all of Germany, so no need for Länder tickets.
Oh, she did say on a Sunday, didn't she (I missed that). Yes it would cost less (€37) with a Schönes-Wochenende-Ticket, but the regional train restriction would still apply, and there would be at least as many (min 3) train changes. Also, the S-W-T is only valid (pg 8, item 5, Schweiz) as far as Basel Bad Bahnhof.
Update: Travel from Basel Badischer Bahnhof to Basel SBB Bahnhof is completely within the district Basler Verkehrs-Betriebe and the fares, whether by train, tram, or bus is one zone, CHF 3,20 (about €2,40) pP.
Here is a schematic map of the Basler transit district.