If you cancel within the 14-day period because someone tests positive -- such as an <5 with the 3-day prior test --
DCL does nothing other than refund your money. If someone in your party (any age) tests positive
at the port, DCL is putting up those folks in a hotel for quarantine. I'm not sure the length of time, it might be 5 days with a negative test or 10 days without. My understanding is DCL has contracts with hotels in their port cities who agree to have guests quarantine there.
It depends on your traveling connection. When DCL was doing embarkation testing of everyone, if the 2 linked parties arrived together both were denied boarding, if the 2 linked parties did not arrive together then only the one stateroom is denied boarding. It is probably based on the honor system with pre-arrival testing.