In general, use only last names on second reference, unless an individual requests otherwise. See also AP Style Arabic Names, AP Style Chinese Names, AP Style Korean Names, AP Style Russian Names, and AP Style Spanish Names.
When it is necessary to distinguish between two people who use the same last name, as in married couples or brothers and sisters, generally use the first and last name. See also AP Style Courtesy Titles.
In stories involving juveniles, generally refer to them on second reference by surname if they are 16 or older and by first name if they are 15 or younger. Exceptions would be if they are involved in serious crimes or are athlete or entertainers.