If you want to know how the Parks are doing, all you have to do is track them by their different homes.
First you've got the house in Korea that "sits like a hen" (4.22), humble and small, but comfortable. Then you've got the house in the ghetto, with "[o]ld brown paint peeling off. Old brown grass flying away. Crisscross metal fence all around" (9.1)—clearly not a comfortable place and most definitely wracked by poverty.
And finally there's the house the Parks (minus Apa) move to at the end of the book:
The patch of grass is so small you can walk across in four long strides. But I don't care. It is ours. I walk barefoot back and forth across the vibrant green lawn, take in deep breaths of air. My toes clutch the tiny blades, revel in the softness and the damp earth beneath my feet. All ours. (30.1)
These houses chart how far—economically and psychologically—Young Ju, her mom, and her brother have come, how hard they've worked and how they've persisted in the face of some serious hardships. So think of the houses as measuring sticks for the Parks's success at self-sufficiency.