Hello Tenessoch46
You can buy Saver Day Passes for Switzerland, but you will need two passes for every person because you stay two nights in Zermatt (one for the outbound trip and one for the inbound trip). Be sure to select the full price without the Half Fare Travelcard. Such passes are not exchangeable, not refundable and are cheaper if you buy them in advance. Children under 6 years old don’t need a ticket in Switzerland, between 6 yo and under 16 yo only a half fare ticket.
You can find more informations here:
https://sbb-tickets.cc/en/tickets-offers/tickets/day-passes/saver-day-pass.html
Between Colmar and Basel, you can buy tickets separately on sncf-connect.com or in the SNCF app. Such tickets are also available on vending machines in Colmar or Basel (French part of the station). Children under 4 years old don’t need a ticket in France.
Kind Regards
Daniel