Testing positive and not being able to leave would make you have to quarantine in Jamaica. If you test in Negril, then you may be placed in the quarantine area rooms that all Covid Resilient properties are required to have available. Before Riu opened, it was being used as a quarantine facility. Now that it is closed again, that relationship may be started again.
Some properties are allowing quarantine for free, others at a reduced price. The government will be monitoring your process to see that you do not develop complications. Just an FYI, for Jamaicans, the vast majority are quarantining at their homes.
If one person tests positive and the other negative, the negative person would be allowed to leave.