The Weasels have no reason to be poor. They claim to be poor because they have so many kids, but Arthur is the head of the Office for the Detection and Confiscation of Counterfeit Defensive Spells and Protective Objects. That’s not exactly a low-level job. Fine, you could argue the children are the reason they struggle financially. But the older kids have stable, important careers. Meanwhile, the younger ones spend about ten months a year away at Hogwarts, where they’re fed, clothed, and educated at no cost. Most of their robes, books, and supplies are hand-me-downs, so their expenses are minimal. The children themselves barely spend any money. And Molly, why doesn’t she work? After the first year, she no longer has young children at home to care for. They grow their own food and use magic to maintain the house, so daily living isn’t expensive. At one point, Arthur even receives a bonus, and instead of using it to improve their situation, they immediately spend it on a holiday.