Can a US permanent resident marry and legalize an illegal immigrant (alien)?
If the immigrant is illegally in the USA and illegally entered the USA, they can not become legal without returning to their country and starting the process there. A Permanent Resident DOES NOT have the same rights as a US citizen. A Permanent Resident can petition for some relatives to join him or her in the United States as immigrants. Those relatives are your spouse and children, regardless of age. You should ask an immigration officer, attorney, or voluntary help organization for advice about this.