American Families United Act This bill amends the Immigration and Nationality Act (INA) to revise waiver of inadmissibility requirements, including by waiving inadmissibility for: (1) certain persons who entered the United States before age 16 who have earned a degree from a U.S. institution of higher education, (2) false claims of U.S. citizenship by persons under age 18 or lacking mental competence to knowingly misrepresent a claim, and (3) false claims of U.S. citizenship if inadmissibility would create family separation hardship for the alien (including a self-petitioner under the Violence Against Women Act) or for a U.S. citizen or lawful permanent resident family member. The bill: (1) authorizes parents of U.S. citizens or lawful permanent residents to apply for a waiver of inadmissibility for unlawful presence, (2) places a three-year limit on immigration-related misrepresentations rendering aliens inadmissible, and (3) revises the definition "conviction" for INA purposes. An immigration judge in specified circumstances, including family separation hardship, but with certain exceptions, may decline to order an alien removed, deported, or excluded and terminate related proceedings or grant permission to reapply for admission or for relief from removal. Nothing in this bill shall be construed to enable the Departments of Justice and Homeland Security to expand their discretionary authority beyond a case-by-case basis or to provide legalization or nationalization of covered persons.