One way of approaching the Hammershoi-like starkness of the Twists' living room with its single wall decoration of a cross and its diffuse lighting, is to contrast this with what we find above in Jack's bedroom.
There, the room has colours and a very varied collection of "things". There's the colourful bedspread and pillow on the single bed - note the reds - the desk with its toys and a rather crude, framed painting of cowboys herding cattle above, (could it be by Jack?), the rifle on the rack, the dresser with the baby boots, clock and covered wagon on top and another painting half seen above, Jack's clothes, and, of course, finally, the shirts. The net curtains are not closed in this room but open, allowing natural light to fall and, of course, the window opens, allowing access to the natural world outside.
I'm not sure where such a contrast might take us but it's undoubtedly there, so I thought it was worth noting.