Thanks for all the inputs. I decided not to chance it, hence booked everything (online) under passenger A’s AM account. This is one of the rare Europe - HKG - SIN routes at only 65K AM each before the 1 Oct devaluation (soon to be 84K!) so we’re pretty chuffed about it!

Reasons for this slightly odd request are:
- Passenger B has some orphaned AM in the account, which happens to be just sufficient for one redemption.
- I thought passenger B’s travel insurance kicks in only when the taxes are charged to their card. But in checking the fine print, it covers also when charged to Passenger A’s card if Passenger B is “travelling together”.