Hello Ruewoirrue92
Yes, every one has to have a ticket. The seat reservation grants a free seat on the train, but not free travel. Children with the Swiss Family Card or the Junior Card travel for free if the parents do hold a valid ticket.
Regular point-to-point tickets or Saver Day Passes are valid on any connection. Supersaver tickets are valid for the chosen connection only.
You have to be in the possession of a ticket for the respective travel class in which you made a seat reservation (or a 2nd class ticket with an upgrade ticket (so-called change of class ticket) for 1st class). Same as on a flight: you cannot take a seat in First Class if you hold a ticket for Economy class.
There is no day swisspass. Whether a Saver Day Pass or a single point-to-point-ticket is cheaper depends on the entire route you are going to travel on that day. You would have to indicate to us the departure / arrival point, the date of travel, and who will be part of your group (age) to give you accurate advice.
Kind regards,
Roland