The advice from the experienced travellers in the community is to use other ways to make reservations than the Interrail/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 topic, and you will get advice. 

Hello, I appreciate that this advice might no longer be useful, but it sounds like some travelers in your group might have a pass limitation. For example, someone might have a One Country Pass when you wish to make a reservation for an cross-border trip. Please feel free to reach out to me or our customer service team if this caused any problems during your trip so that we can investigate this issue :)