You can buy tickets for more than one traveller in the SBB Mobile app, by adding the passenger and editing the data before you proceed with the purchase. Both tickets will then appear on your app (Section “Tickets & Travelcards”). Here you will find more information.
For each Half Fare Card, you will receive a confirmation e-mail with a copy of your pass, which you can show during ticket inspections. All you need is to have access to the mailbox from the mobile phone you will be using (or you can save the two digital passes on your phone). Or, if you create an account on SBB.ch before purchasing, you can view your Half Fare Card by logging into the SBB Mobile app with the same email and password.
I wish you an amazing stay in Switzerland.