To clarify: It's one OBB benefit per cruise per household address. A family could have more than one household address, and, thus, be able to book more than one set of reservations/placeholders.But as the PP said, only one OBB benefit per cruise per family.
If someone is allowed to do it, they are lucky. The restrictions say "per household sailing". Even if that address is spread between multiple rooms.YMMV but a family, with one household address, split into two staterooms can also book two sets of reservations/placeholders. The system allows it. The onboard future cruise planner may disagree, but the system allows the booking to be made.