My friend and I tried it several years ago, and it didn't ever work correctly. All of our charges kept going to my friend's credit card (she as the one whose name our reservation was under, and she had used her credit card to make the room reservation). This happened even though we both set up separate cards and PINs on our own magic bands. It was very frustrating, I had to keep going to the front desk and separating my charges out each day. The front desk kept assuring me that they had fixed it each time, but every day it happened again. After three days of this, I gave up and stopped charging to the room using my magic band.
This problem might be fixed now, where multiple people in the same room can set up their own credit cards and PINs on their magic bands, but you might want to figure out a back-up plan. It's such a pain to figure out whose charges are whose!