You would discuss it with your MD well in advance before your friends/family/significant other visits you, and they will tell you the proper way to handle it. I think you need to talk with HR and with the staff captain. This would have to be done well in advance; if you spring it on them when your guests arrive, they’ll get suspicious and just assume that you just met the passengers on embark day and are trying to pull a fast one on the company. They will usually understand.

If it’s a significant other, I’ve seen crewmembers with their own cabin just have that person in the room with them, for a highly discounted price for the cruise. If they get their own guest cabin, you have to sign some paperwork allowing you entry into that particular cabin, I believe.

In short, it can be done, but there will be some procedures to go through.