The Sustainable Homeownership Act aims to enhance homeownership opportunities while ensuring financial stability in the mortgage market, specifically focusing on the roles of Freddie Mac and Fannie Mae. The legislation introduces new requirements for mortgage insurance and guarantees, particularly for loans exceeding 80% of a property's value. For instance, if the unpaid principal balance is between 90% and 95% of the property's value, at least 30% must be insured, with higher percentages required for even riskier loans.