We were in Prague once towards the end of February, and we had a wonderful time. Days were cold but sunny, and there were much less tourists than when we previously visited during September.

I absolutely love Salzburg and have been there twice, but not sure that you need three days there. I agree with the suggestion to do it as a day trip from Munich or use it as a stopover (one night) on the way to Berlin. Re-apportion Salzburg days to other cities to give you more time and less of a rushed feel. Because this itinerary just seems SO rushed, if I were you I'd definitely cut Krakow and either Berlin or Amsterdam. That'd make this trip much more manageable!

I will say that I've lived in Prague during the winter (February included) and while it IS extremely cold, I actually prefer it in the winter! So many less tourists, so you really have the city more to yourself! It gets so crowded in the spring and summer that it can be less enjoyable. So don't worry too much about not enjoying yourselves in the winter - you'll have a great time! Just please pack heavy winter coats and gloves/scarves.

3 days in Salzburg means they could take the Sound of Music tours to the famous Lake district just east of town - easy to do on own by post bus from Salzburg.

Your list seems a bit long, besides you forgot to count the time to be taken for the road to each city. I think it would be better if you remove some of them from your list. Munich and Belgium are musts here due to the flight routes, others are up to you. I went to Germany last Christmas and it was great! The weather was cold that time, I believe it's a little warmer and more rainy during February/March.