BUR #44058 has been approved by @Hillside_Moose.
create alias asako_(hikaru_ga_shinda_natsu) -> yamagishi_asako
create alias hikaru_(hikaru_ga_shinda_natsu) -> indou_hikaru
create alias yuuki_(hikaru_ga_shinda_natsu) -> tadokoro_yuuki
These are the official full names of the characters. The official anime site lists them for Asako and Yuuki (with the furigana if you click the JP language option), and while it doesn't list Hikaru's family name there, it's in the manga itself and various other places like Wikipedia and such.