I think Mark Dunn has mistaken what TfL meant by separate cards/devices.
To TfL, they see separate numbers for each card/device as they all have original or virtual card numbers. TfL doesn’t care which account it’s debited to as long as the payment request goes through, as it’s alluded in this paragraph:
If you have a joint bank account, you can usually both use your contactless cards to travel as each card will be charged separately.