You book in each train the number of seats depending on how how many people travel together.

For Sweden: sj.se

For Denmark to Germany (mandatory reservations): cd.cz (€3.10 per train)

For Germany: bahn.com (4.90 per journey) or tickets.oebb.ar (€3 per train)

If you need specific advice about reservations, please mention route, date and departure time.

To plan international journeys, bahn.com is a good tool.

If you want to use a night train, then book it ASAP.

Passes and seat reservations are totally separate so it doesn't matter if you travel together or not.

Simply book for 4 if you're 4 and 5 otherwise. Seat reservations are best bought elsewhere than interrail.eu (extra fees). Have a look at those helpful links :

https://www.seat61.com/interrail-and-eurail-reservations.htm

https://community.eurail.com/train-connections-reservations-47/how-to-get-reservations-105

Mandatory seat reservations between Germany and Denmark are best bought through cd.cz : 73 CZK or 3.10€.

There are also night trains between Berlin, Hamburg and Copenhagen + Sweden : sj.se and snalltaget.se. Please note that they're very popular so book ASAP.

Do not hesitate for questions.

What are your travel dates?

The night trains between Germany and Sweden, SJ and Snälltåget, are mostly sold out during the summer. Between 21/7 and 31/7 no night trains are running due to construction works in Denmark.