It's your choice whether you have both passes on 1 device or on separate devices. If they're on 1 device though, you can't travel separately.

Each pass has its own trip. The trip is stored on the device and a change to one trip doesn't automatically change the other. If the passes are on the same device, you can add a journey to multiple trips at the same time.

Whether you're logged in or not in the app doesn't make a difference. If you're logged in, then you can see in the app any reservations you made on the Eurail website. That's however the last place to book reservations, because of multiple reasons, one of which is that it's more expensive than elsewhere. Instead, use this page as a guide:

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

In addition, the app should not be used to plan because it's incomplete, often out of date and generally unreliable. Instead, use national websites or apps; for international travel, www.bahn.de or the DB Navigator app is a good choice.

Many thanks, that answers many questions.

Sorry, another question. Where is the best place to book the reservation? Rail Europe? I couldn’t see a place on the babn.de website to use the pass. Thanks

On bahn.de, you can check "Book seat only”. However, it can only book some reservations. There's no website that can book all reservations.

Where to book depends on the train and that's where the pass reservation page on Seat61 that I mentioned comes in: it explains what trains can be booked where. If that doesn't help, you can ask here but you'll need to mention route, date and departure time.

Thank you, much appreciated.