How do I get the house my mother left if her husband does not want it?

Your brother, as personal representative, has the obligation to distribute the remains of your mother's estate (after all outstanding bills and expenses are covered) either according to her will or according to the laws of intestacy. If your mother's husband doesn't want the property and you're not entitled to it either via a will or intestacy law, you can make an offer to the estate to purchase the house on your own.