You will find this arrangement very cramped. definitely not suited to an extra adult. We have occupied similar cabins (2 of us) on Navigator of the Seas and the cabin is adequate for 2, albeit with limited storage space, but for 4 of you it will be a real trial. My advice would be to book 2 interior cabins, perhaps on a lower deck. (There is little difference in cabin size for inside cabins.
Thanks. 2 interior cabins was costing more than a balcony cabin for 4, as in 2 cabins you don't get a reduction for 3rd adult and child. Will maybe try for an upgrade to a bigger 4 berth.
Even a bigger cabin would seem "Crowded with 3 adults and a child! As you say in your question, "We only use it to sleep in" is correct, I would stay where you are, save your money.
You can always see Guest relations and say, "Should there be a chance of an upgrade will you keep us in mind" Explain and be "Nice" works wonders.
Thanks! We will take your advice ....unless , of course, we win the lottery between now and next July..in which case we will go for the presidential suite! Our travel agent has advised to wait until the balance is due as there may be cancellations, but they also said that, as we booked really early, we actually have one of the best interior 4 berths and it is very well placed, so will stay put just now. Thansk again for your help