Train passes in Munich

Dachau is in the MVV district, so it is a local transport ticket. Center of Munich to Dachau and back would be a 20.10 EUR M-1 Gruppe Tageskarte for an all day ticket covering 2 to 5 people traveling together.

Munich to Mittenwald and back in a day is a Regio Ticket Werdenfels. Cost is 39 EUR total for 2.

For travel in Munich (MVV):
The map of the travel zones in Munich is here.
Almost everything you will want to see in Munich (exc Dachau) is in the M, central district of Munich. Dachau is a border station between zones 1 and 2. From the M zone to Dachau you will need a ticket that includes both the M and 1 zone, M-1.

Here is the table of fares for Munich:
As long as you are staying in the M zone, a single trip ticket is 4,10€. This would cover a single trip ticket by any conveyance, regional trains, S/U Bahn, streetcars, or buses. A round trip would be 8,20€. For only a little more, 9,70€, you can get a Single Tageskarte (all day ticket for one person) which will allow you to ride any conveyances all day long until 6am the following morning. The same ticket for up to 5 people is 18,70€.

For travel to Dachau, you need a M-1 Tageskarte, for 6,10€, 11,10€, & 20,20€ respectively.

As for travel to Mittenwald or Innsbruck, you can use a Werdenfels ticket (to Mittenwald) or a Werdenfels + Innsbruck ticket (if you go to Innsbruck via Mittenwald). The Werdenfels ticket is 29€ for the first person, 10€ more for each additional person up to 5, total. The Werdenfels + Innsbruck ticket is 35,50€ for the first person, 16,50€ more for each additional person.

The Werdenfels ticket are for one day only, so you must complete the round trip in a day or get two Werdenfels tickets.

You could buy a Eurail pass, but that’s a very expensive option for your trip.

How many are “we”? There are day passes you could use that are good for up to 5 people. For example, for the Mittenwald day, you could use the Bayern Ticket (valid after after 9 am on weekdays, all day on weekends) for €42. Dachau is a local trip, so it’s cheaper, about €20 for a group day ticket. If you use the DB Navigator app or MVV app (Munich’s local transport app) and plug in your journeys and number of people, the prices will appear.

The Munich airport is about 45 minutes away, and a group day ticket will be €30 to get you to the city center. If you’re just using the metro in the city center, the group day ticket is about €20.

You’ll need to book the Munich to Zurich journey separately on either DB or SBB.

Don't worry about all the fare zones and day tickets in Munich and its transport network; that's yesterday's expertise. Just download the MVV app or the MVGo app and use the “swipe in/out” function. This means that before you board the train, you log in (the system recognizes your boarding point) and when you leave, you log out. If you forget to do the latter, the system will remind you five minutes later and if you don't respond, it will log you out automatically. You will be billed at the end of the day and you will pay a maximum of the price of a day ticket.

For the trip to Mittenwald, take the “Regio-Ticket Werdenfels” mentioned above from the ticket machine, which is not subject to the restrictions of the Bayern Ticket and can be used at any time.

I just finished researching the same for my upcoming visit to Munich. I agree with Fritz about MVVswipe / MVGO app. Seems the easiest to use, and it is supposed to figure out the lowest cost fare for you that day (single tickets, day ticket...not sure about group ticket). Also saves the trouble of figuring out fare zones ahead of time or at ticket machine. The app will also give you ticket suggestions that you can purchase, but if using the app anyway I figured I would try MVVswipe.

I was able to register and enter credit card payment information. I registered via M-login which I guess is a broader thing than just public transit. I used a desktop computer for the credit card info.

Proof will be in few weeks LOL.

The Werdenfels ticket also covers use of regional trains and the S-Bahn (but not U-Bahn, trams, or buses) in Munich metro, and regional buses in the Werdenfels region of south-western Bavaria. See map.

that's yesterday's expertise

I guess I'm showing my age. I was in Munich three times in the eighties, and I've been there five times since 2000. Most of this travel was before apps. I got used to using the ticket kiosks; they're no puzzle to me. In fact, although I do use take my cell phone to Europe with me now, it stays in my suitcase until I come home, to call for transportation. In Europe, I use my pad with wifi (it has a much bigger screen and a real keyboard).