You do not book anything in Switzerland. Tickets can never sell out.
On the day you choose which train you'd like to take and add it to the app before you board. Then you enter the train and sit wherever you want. You do not "book" anything, the Eurail pass is your ticket.
Use SBB app or sbb.ch to get an idea of all the connections.
1. Lucerne - Engelberg + walk to the cable car. Buy tickets there.
2. Lucerne - Interlaken Ost train and then either via Lauterbrunnen or Grindelwald. Book tickets from Interlaken Ost through jungfrau.ch or at Interlaken train station (same price).
3. Weggis does not have at train station. Bus to Küssnacht am Rigi (not included) and then train or boat to Lucerne (50% discount)
4. Cable car Weggis - Rigi and back Rigi - Vitznau cogwheel railway or the other way around (50% discount). Vitznau - Weggis : bus (not included) or boat (50% discount)
5. Lucerne - Brienz train and then boat. Everything is included, you only add the train and the boat to the app before boarding
Again please use the SBB app and Google Maps to find the nearest stop from your hotel
