IMO, the studios were designed for singles or couples. While they'll allow you to book one with 4 + a baby, it wouldn't be my idea of comfortable. I, too, think you'd be much more comfortable in a bunk bed room at AKL or WL. There's virtually no room to walk around in a studio with the sofa bed open, and you'd need to put the crib in front of the bathroom or in the door/entrance area.
A bunk bed room will feel much more spacious, there'll be more room for the crib, and the kids can nap without having to open up the sofa bed.