Multiple Room Bookings and Receipts
For multiple bookings, booked at the same time, the Credit Card is always attached to the last booking in a series. Thus, if there is a 123-1X (the first room booking), and a 123-2X (the 2nd room booking), the 'receipt' is issued against the last bookings in the amount equal to the deposit. Also, this last booking in the sequence is where the credit card would be stored.
So, in the case here, the 123X-2W booking will have the deposit/receipt issued against it. This single receipt must then be allocated to the 2 bookings manually, by staff, if using the PMS'.
Using XML, you are able to to break up the multiple transactions into separate bookings, if you desire. If this were to happen, there would never be 123-1X and a 123-2X, there would only be 123X (the first room booking), and a 124X (the 2nd booking). This approach allows your XML app to save each booking individually and allocate the desired deposit and credit card details to each booking.
The work to do this more complex, and for the few times there are multiple bookings done in a single transaction, not very likely to be worth the effort.