What requirements are you talking about?
U.S. Immigration Law
First they have to obtain a green card. That requires proof they will not be a welfare mooching public charge. Public charge refers to becoming dependent upon the government for the expenses of living (food, shelter, clothing, etc.) Second they must show proof of medical examinations and vaccinations that proves they are in good health.
That's just for a green card. After 5 years on a green card then they can apply for citizenship and get back in another line. That will require being able to read, write, speak English. Understanding of U.S. history and government. No serious crimes committed.