The tickets aren't personalized (some regular monthly passes for public transport are/were though), so you should be fine. Since they aren't personalized and there is no way to check who the owner actually is, I would even expect them to be transferable.
Edit: looks like I was wrong -> see replies. You can also search for "9-Euro-Ticket übertragbar" (übertragbar = transferable) yourself to get a number of different German sources for that.
Normally DB day tickets, even bought at the ticket machine, are not transferable. You have to write your name on the back - in theory, before the first time you encounter a ticket controller - and be prepared to produce ID matching the name.
Edit: looks like I was wrong -> see replies. You can also search for "9-Euro-Ticket übertragbar" (übertragbar = transferable) yourself to get a number of different German sources for that.