You can book these reservations at many ticket offices that can do international reservations. Try in Belgium when you get there. It will also be a lot cheaper than via Interrail. If that doesn't work, then try in Germany.
Alternatively, you can call DB (+49 30 311682904) and then collect the reservations at a DB ticket machine when you get to Germany.
The reservation Prague to Katowice can also be made online via Czech Railways. Add 4 persons, look for the connection and then click on "I want a reservation only”. Price per person is CZK 76 (~3€).
The night train unfortunately currently does not work for online booking.
You are a SUPERSTAR!!! I’ve made the Prague to Katowice booking as you advised & if there are no online options, then I’ll try book the overnight when we get to Belgium as you advised.
You’ve made my day - thank you!
Hi there
When I was looking to book something else just now, I saw what appeared to be a new message in website that said that trains going into or out of Austria could be booked via OBB website. I’ve just followed all instructions but when I get to the train that I want 22:49 from Krakow Glowny on 2 Aug arriving at 7am in Wien, it tells me ‘ticket not available’. How do I know please if that means that they are sold out of tickets or that I just cannot book it online with them? Any ideas?
The connection with the Polish reservation system hasn't been working well for quite some time, which affects all bookings within Poland or starting in Poland. The best is to book this reservation at a ticket office, e.g. when you get to Austria. Should also work in other countries, e.g. Germany.