Debtors’ household included parent living with debtors who contributed a portion of Social Security income to household expenses and who was physically impaired and dependent on debtors for care. “At least three analytical approaches have been judicially developed to determine household size: the Census Bureau “Heads on Beds” approach, the IRS dependency approach, and the economic unit approach. . . . [T]he result is the same under each. Barbara’s mother is actually residing with the DEBTORS on a permanent basis. She is making a financial contribution to the household and her regular living expenses are paid from the household’s combined income. She is part of the economic unit. In addition, she is actually dependent upon the DEBTORS and is claimed as such for tax purposes.”