seat reservations needed?

A group of 4 adults will be traveling in Switzerland in late August - early September. We have 2 legs of travel that concern me... Interlaken to Luzern; Luzern to Zurich Airport. Because these are busier routes, will we need to reserve seats? We each will have 1st class Swiss passes.

In my opinion seat reservations are not needed on either train especially the Luzern to Zurich Airport.

Both trains originate in Luzern so get to the platform about 15 minutes early and you will not have any trouble

Dick