A lease to own gives you the option to buy...so it wouldn't be a refinance, it would be a purchase.
Unless you have 20% to put down or more, there is no way you can get a loan with that low of a credit score.
Keep in mind that if your credit score hits 500, that is the number banks stop lending on.
I think your family needs to move into an apartment that you can afford, rework your family budget, and pay off your credit cards/collections...b/c you don't get a 520 score by paying your bill on time.
Realtor..see profile for more.