Sometimes on NCL, Celebrity and RCI, a reduced deposit is offered, but not often. Can't recall when I have seen it offered on CCL.
Sometimes a reduced deposit is available for a "Group" booking, but again, not always and usually must be a large group.
Traditionally, a 7 night cruise will require a $250.00 p/p deposit with most cruiselines.
This far out, perhaps you could "try" to book a stateroom that can accommodate 4 guests, but only book with 2 passengers to start with to ease the deposit and then add the 3d and 4th passenger to the booking at a later date when the finances are atad better. But many cruiselines will not allow 2 passengers to book in a stateroom that is designed to accommodate 4 guests, especially if during a peak season of cruising or holidays.
If you are able to do the suggested scenario of booking 2 pax in a quad stateroom and then add the other passengers later, you risk the chance of that 3d and 4th passenger rate going up and or the ship having already exceeded 3d and/or 4th passenger restrictions (again depends on when you add those other pax).
Good luck !