If all involved are ok with it, you can add their booking to your cruises through Manage another booking (on the right of the page) in your Booking & Order Details tab. This would list their booking along with yours and you would see all that they see such as what they have purchased, excursions booked, fare prices, etc. I have adult children that have authorized me to do this so that everything can be booked together. Their bookings then came up for Specialty Dining and other purchase options. An extra way we all benefitted was that I was able to check all of the cabins in at the same time so our boarding times were together. They logged in the day after check-in and added their own cc info for onboard spending, ID info, and anything else I skipped during check-in. The Skip option came in handy.
The drawback is that I was unable to find a way to remove their booking from my list. This was not an issue for us but it may be for others.