Any member of your family is working and income is more than 20K dollars, it's hard to get it. They will ask you to show three month Bank statements. You can imagine in this case what ....
After moving into the new house, and you start to pay your mortgage. From then on, waiting for three months, maybe you can try to apply for the "房顶". Or you can transfer your money out, and make sure not too much money left in your account statement for three months.