Yes, I remember replying to you in your other thread(s) about this.
Don't worry about the stateroom arrangement for this part; it really has little to do with what you're trying to do. Each person will have their own onboard account, and their own folio (bill). Again, this happens regardless of who/how many are in each stateroom, so don't worry about that.
It sounds like you want to be able to use 4 different credit cards, one for each person. You can absolutely do this. You can either enter the credit card info (for each person individually) during online check in, or to your earlier question, you can put 'cash' for them during online check in, then go back and update with credit cards numbers later (or once onboard).