Right now the Burbs live in a small apartment across the Oldie's because they just didn't have enough money to buy their dreamhouse. They want to save a bit first, but Lucian is growing and with rent coming every month, it won't be sure they can save all that much.
Also Joan really wants another baby (or maybe 2 or 3 or 4 or ...) and then the apartment is going to be really small. So Jeremy decided to work even harder to find a house where they can live very rich.
But will Joan like the house enough for the big family she wants? What will Lucian say when he hears there might be a baby (or 2) coming? And won't they miss it too much to live across the hall of the Oldies (= easy babysit)?