Hello Lueraco22
You cannot add the Swiss Half Fare Card to the SBB Mobile app, you have to present it separately, either as print-out or as part of a PDF.
However, when buying tickets with the app, you can check the ½ fare option with your personal details. See the pen icon above the ticket selection. On the Profile tab, you can find the Co-Passenger option; there, you can all your co-travellers in order to purchase tickets for them.
Please kindly note, e-tickets do require a physical passport or national ID card; you must present it together with your tickets upon ticket check.
Kind regards,
Roland
