To the OP, very sorry about your situation. As a physician (critical care), I have to agree that using a PCR for pre-cruise testing is overkill and will pick up far too many asymptomatic and recovered patients. In the hospital, we know how extremely sensitive PCR is and stratify positive patients based upon the PCR cycle threshold (CT value) to determine whether they are infectious or not.
I cruised on Virgin last month and antigen testing at the port was quick and easy, plus you can have the added comfort of performing a home antigen test prior to leaving. Granted, no kids on that ship, but I think antigen testing would be more than adequate for
DCL.