Both tickets must bear the name of the respective passenger, including date of birth. Or in other words: each passenger must have its own ticket bearing his/her name & date of birth.
Two tickets bearing one and the same name for two passengers is not possible. For every passenger without correct ticket, during ticket check, passengers have to buy a new ticket and pay a surcharge (penalty) of at least CHF 90 per person without valid ticket.
If you are an agent or an assistant, you can enter the passenger information upon purchase. If you have got an account yourself, you can add other people as co-travelers in your account and only buy tickets for them by unselecting you as passenger (who is travelling) during ticket purchase.
Tickets that you bought as guest cannot be added to the SBB Mobile App. It only works if the tickets were bought using the passengers personal SBB account.