Names of the children in the family register in order:
1) Jang HaMyeong May 20, 1983 29 years old
2) Jang HaSeon February 23, 1985 28 years old
3) Jang HaJin May 15, 1987 26 years old
4) Jang RaHee February 15, 1989 23 years old
5) Jang RaGong March 14,1990 23 years old
6) Jang EunSeong (HaNa) December 5, 1990 23 years old


взято с forums.soompi.com/
правда тут пишут RaHee and HaJin's age difference is over 2 years.
But in the first episode, the young HaJin looks 5 or 6 years old and RaHee is still just a baby.