Can I book trains without activating my passes? We don't have our passports yet

You can make reservations without an active pass.

The advice from the experienced travellers in the community is to use other ways to make reservations than the Interrai/Eurail website. You can look at the guide in the link:

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

If you, after having looked at the guide, have questions about how to make specific reservation, please give your travel details (departure date, time and route) preferably in a new post, and you will get advice.