The situation never arose in fact so the answer is moot. We did, however have "a bit of fun" using the ticket.
It was a bit of a struggle to get the right ticket issued at Sheffield in the first place. We were initially quoted a lower price (£18-odd?) each. Not knowing exactly what that ticket was we declined and after intervention by another member of staff eventually found the right thing. As stated in the website T&C we were issued one paper ticket which clearly stated "2PPL" on it.
We travelled on a through train from Sheffield to Scarborough and returned breaking our journey in Hull. We were inspected three times during this itinerary.
Conductor 1: QR code scan, looks at reader screen, and asks where the other person's ticket is. Pointed out the wording on the ticket; "OK, fine, thanks".
Conductor 3: ditto.
Conductor 2: No, you should have been issued a ticket each. Hostile manner. Pointed out the ticket wording and described the website T&C as being the reason we weren't expecting to get two coupons. No change in attitude or position. S/he showed me the QR scanner screen which stated on it "One Adult" (which presumably explains the reaction in all three cases) but when s/he tried to hide behind "I've been doing this job for x-teen years" I lost any confidence. QR scanners have not been around that long, and this ticket has only been on sale for a month or so - so where's the relevance?
Anyhow the conversation ended with my asking, pleading, with him/her to please go and check independently. Grunted hostile response to that and no eye contact.
However some time later s/he returned to our seat with an apology. S/he had actually done some checking and had seen the same website's T&C. So, right outcome in the end, but that initial hostility wasn't justified.
Whoever coded the screen response on the QR machines has got that bit wrong. How long before it's corrected and how long before someone has to go through the rigmarole of contesting a penalty?