Train from Garmisch to Munich, Munich to Salzburg

"We will be taking train from Garmisch to Munich on a Sunday morning..."

Use the Werdenfels Ticket instead. At €23/2, it's good for Garmisch-Munich and costs less than the Bayern Ticket (€29/2.) (Also, it's valid on any day at any hour - no weekday 9 am restriction.) Buy it at the station.

In German: http://www.bahn.de/p/view/angebot/regio/bayern/regio-ticket-werdenfels.shtml
Werdenfels Ticket routes: http://www.bahn.de/p/view/mdb/bahnintern/angebotsberatung/regio/regionale_tickets/mdb_200857_karte_regio_ticket_werdenfels_sept_2015.pdf

You'll need the Bayern ticket for Salzburg. Buy it at the station too.

For Munich to Salzburg, you can use Das Guten Tag Ticket for 26€ (21€ + 5€) for 2 people.

Regional trains from Munich to Salzburg, Kufstein, and Holzkirchen are run by Meridian, a subsidiary of Transdev, under the privatization policy of the Bahn. Meridian's sister subsidiary Bayerische Oberlandbahn (BOB) runs the trains in the Bayerisch Oberland south of Munich, with three branchs emanating from Holzkirchen to Bad Tölz, Tegernsee, and Bayerischzell. The Guten Tag Ticket is valid in both systems, just like the Bayern Ticket.

Unlike the Bayern-Ticket, I don't think the Guten-Tag ticket is valid for transport inside Munich. You will need to find you own transportation to Munich Hbf, Munich Ost, or Munich Grafing, where the Meridian trains stop.

The Werdenfels-Ticket is valid for the S-Bahn in Munich.

Thanks Lee and Russ- I think I get it now!
We are staying close to train station in Munich so that bit is fine.

Werdenfels ticket from Garmisch to Munich and can use it on S-bahn that day as well- correct?
Das Guten Tag ticket Munich Hbf to Salzburg Hbf

Looks like both have about hourly connections.
Assuming the ticket machines are easy enough to use at stations and these options will be clear?