travel from Rothenburg Germany to Munich then on to Hohenschwangau and Disn

I assume you are a single traveler. You can travel by regional train from Rothenburg to Munich, a little over 3 hrs, for €20 with a Bayern-Ticket Single. If you go onto Hohenschwangau the same day (really wouldn't advise it; Munich is worth some time), you can use the same Bayern-Ticket for the train to Füssen Bahnhof and the bus from there to Hohenschwangau. Otherwise it's another €20 Bayern-Ticket for Munich to Hohenschwangau.

What's Disn?

I think he wanted to say something about "Disneyland castle" (Neuschwanstein) and ran out of space

BUS? The Romantic Road bus? It's 43 Euros one way R'burg to Munich and requires a 5-hour bus ride that makes only the most minimal of stops in the RR towns along the way. Now, that might be cheaper than renting a car, but it's not the best or cheapest way to get to Munich. That would be the train.

Thanks to you all

If you want to get a feel for the Road and see two of the most scenic towns, there are bus connections via the road that's designated as the Romantic Road from Rothenburg to Nördlingen via Dinkelsbühl. You can leave Rothenburg in the morning, spend a couple of hours in each town, then take the train from Nördlingen to Munich in the late afternoon. You'll miss Füssen, but you are going to do that another day, anyway. . . . . . ¶ If you use a Bayern-Ticket, it will cover the bus from Rothenburg to Dinkelsbühl, and at least part way from Dinkelsbühl to Nördlingen, to the border of the Verkehrsverbund Grossraum Nürnberg (VGN, Greater Nürnberg), and it will also cover the regional trains from Nördlingen to Munich. I'm not sure about the section to Nördlingen (Verkehrsgemeinshaft Donau-Ries, www.vdr-bus.de), because when I did my Romantic Road trip, I only went Nördlingen to Dinkelsbühl (€4,50) to Feuchtwangen (€2,60) that day. It was a lot less with point-point bus tickets than with a Bayern-Ticket.

last time I did munich to Rothenburg I took trains and had to change trains 3 times. It was kind of a pain but doable. I would suggest a bus though if there is a direct one.

Most direct rail connections from Rothenburg to Munich have two changes, Steinach and Treuchtlingen. The only direct bus is the Romantic Road Coach, and it makes only one run a day.