So this is how you do this:-
On the on line checkin there is the options for putting a credit card against your stateroom account.
There is an option for one credit card to go against everyone in the room,
Or
You can out a different card against each person, or say two on one card, one on another.
No need to call
DCL just update the on line check in.
Even if you have completed OLCI already, you can go back and edit it and change it.
Lastly at port it can be changed and at guest services, but online us best pre cruise.