Hello Shoumboorreph73
The tickets, travel cards, and travel passes do show up in the SBB Mobile app of the buyer only. They cannot be transferred to another account.
If your co-passenger wants to use their own card, you can forward them a screenshot of your QR code (or you share your credentials/login with them, to use the same account).
What concerns the purchase of further tickets, you can continue to purchase them for both if you; or, your co-passenger purchases the tickets for themselves, while you show both Swiss Half Cards, or the co-passengers show the QR code, as I mentioned beforehand.
Do not forget to activate the half fare option in each passenger’s profile. The how-to I described in a fellow passenger’s response:
https://community.sbb.ch/d/26418-how-can-i-save-the-info-of-swiss-half-fare-card
Important: when ever you travel with e-tickets and/or the Swiss Half Fare Card, you must also show your physical passport or official ID card; photos on smart phones or paper copies are not accepted.
Does that make sense?
Kind regards,
Roland