Yes, charges are summarized on the cabin bill by person. Some things are put on per person automatically (gratuities); excursions are billed to the person going on the excursion (even if you book excursions for everyone in your group, they get split out to the individual level), other charges are based on which KTTW card was presented for payment (drinks, shopping, etc.)
You can each have your own form of payment (each of you have your own credit card on file for charges to your onboard card). If you do have an OBC, these are typically applied to the first name on the booking so if you are sharing, you may have to work that out.