We just went through this. We took our adult children and their families, we had 3 cabins in total. I had originally set all cabins up connected to my CC. We were paying for excursions so it seemed easiest. I just told each of them that anything else, they would be responsible for, make sure they stopped at the desk and made a payment every few days if needed. They took control and did just that, I didn't worry past that point. I was able to stop at the customer service desk and get copies of room charges when I wanted to check up, since my CC was linked to the cabins they never questioned it.
As mentioned above, you could also set the accounts to cash and just apply funds from your CC to cover things you wish to pay for like excursions. It's all about what's easiest for you.
Just enjoy your cruise. When they are adults, having the family with you is the best! It doesn't happen all that often, they all have 'better' things to do.