Hello lolitajimmy92
Yes, each passenger from their 16th birthday would need their own Swiss Half Fare Card. They are personal. Children 6-15.99 years of age, travel at half fare by default.
The Saver Day Pass can be used at will on the entire Swiss public transit network, and not only on a certain train. The ticketing system offers that ticket because it is the most cost-effective for your journey (less costly than a point-to-point ticket). As it valid for any train / connection, it does not indicate the route nor any train. It allows hop on / hop off as you like, so a seat reservation would not be very helpful. And, you need to specify the route in order for the ticketing system to calculate the best fare.
Even standard tickets do not indicate the train you have selected, as it can be used for any train on the selected day and route.
In addition, please see my other reply:
https://community.sbb.ch/d/7494-1-day-travel-pass-and-saver-day-pass-it-is-same-pass/4
Seat reservations are optional on Swiss trains. You may want to read our blog post on seat reservations on Swiss trains to understand the seat reservation logic:
https://community.sbb.ch/blog/23887-demystifying-seat-reservations-on-swiss-trains-a-comprehensive-guide
Kind regards,
Roland