Their names are Sue (Sook-ja 숙자 淑子), Aija (Ae-ja 애자 愛子) and Mia (Min-ja 민자 敏子).
Sue and Aija are real sisters, and Mia is their cousin.
When they were born, the Korean Peninsula was a part of Japan,
and that is why their names follow the Japanese style (○子).
Mother of Sue and Aija was 이난영 (李蘭影), a singer.
〈木浦의눈물〉(1935) is a great record. https://www.youtube.com/watch?v=glVY1bMICQw
She got married in 1937, and bore seven children.
In 1943, 金海松, 李蘭影, 張世貞 and 金貞九 showed live performance
in front of Prince 李垠 and Princess 梨本宮方子 in Tokyo.
Listening to 〈落花三千〉, Prince quietly cried, they say.
Bonus.
李香蘭 was cast in 「君と僕」(1941). 金海松 was a music staff of the movie, and 金貞九 was cast.
Sue was born in 1941. Sue's real name Sook-ja 淑子 is same as 李香蘭's real name Yoshiko 淑子.
I wonder if it is just a casual coincidence.
