On my recent stay at the St Kitts Marriott, I had 2 devices connected. The system would not allow a third - don't know why. I switched from wifi to wired using my travel router and was then able to use all three devices in the room. (I had a laptop and iPhone and my wife had her iPhone - hence 3).
At check out there were charges for two internet connections for a week each. As a Platinum Member, both charges were promptly removed. No issues at all.