It depends whose credit card is on file for the room. If you made the reservations for both rooms and during check in online you put your cc, you'll be charged
The charges should show separately on each participant's stateroom account - so your stateroom will show 1 charge and the other person's stateroom will show another charge. As PP points out, what credit card is charged will depend on how the stateroom accounts are set-up.
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