The ‘Have It All’ package cannot be shared between stateroom occupants. If ‘Have It All’ is purchased, all guests (age 18 and older) in the same stateroom must purchase the package as well — including 3rd and 4th guests.
Because ‘Have It All’ is designed as a stateroom-level experience, it needs to be consistent across the adults traveling together, so the package cannot be shared by only one or two people while others opt out. It keeps things simple once you are on board so nobody has to do the awkward, “Wait, which benefits are mine?” dance.
If you are looking to add ‘Have It All' after you have already reserved your cruise, you can do that through the options provided in Manage My Cruise. It can also be added after the cruise has begun, though purchasing before embarkation day offers better value.