So I wanted to share this long running list of idols who have siblings that are also idols/actors/actresses!
Note: I won't be listing idols with non-idol siblings. EX: Yongguk and Yongnam
Doyoung & Gong Myung

Gong Myung:
Real Name: Kim Dong Hyun
Birthday: May 26, 1994
Group: 5urprise (he's also an actor)
Agency: Fantagio Entertainment
Doyoung:
Real Name: Kim Dong Young
Birthday: February 1, 1996
Group: NCT (NCT U, NCT 127)
Agency: SM Entertainment
Zico & Taewoon

Zico:
Real Name: Woo Ji Ho
Birthday: September 14, 1992
Group: Block B/Solo
Agency: KOZ Entertainment
Taewoon:
Real Name: Woo Ji Seok
Birthday: May 11, 1990
Group: Speed (Formerly), Currently Solo
Agency: Million Market (Division of SM Entertainment)
Yuna & Seoyul

Yuna:
Real Name: Seo Yu Na
Birthday: December 30, 1992
Group: AOA
Agency: FNC Entertainment
Seoyul:
Real Name: Seo Yu Ri
Birthday: November 26, 1997
Group: Berry Good
Agency: JTG Entertainment
Chaeyeon & Chaeryeong

Chaeyeon:
Real Name: Lee Chae Yeon
Birthday: January 11, 2000
Group: IZ*ONE
Agency: WM Entertainment
Chaeryeong:
Real Name: Lee Chae Ryeong
Birthday: June 5, 2001
Group: ITZY
Agency: JYP Entertainment
Jessica & Krystal

Jessica:
Real Name: Jessica Jung
Birthday: April 18, 1989
Group: Girls' Generation (Formerly), Currently Solo
Agency: Coridel Entertainment (In Korea), United Talent Agency (In US)
Krystal:
Real Name: Krystal Jung
Birthday: October 24, 1994
Group: f(X)
Agency: SM Entertainment
Sungyeol & Daeyeol

Sungyeol:
Real Name: Lee Sung Yeol
Birthday: August 27, 1991
Group: Infinite
Agency: Woolim Entertainment
Daeyeol:
Real Name: Lee Dae Yeol
Birthday: February 11, 1993
Group: Golden Child
Agency: Woolim Entertainment
Yena & Sungmin

Sungmin:
Real Name: Choi Sung Min
Birthday: December 7, 1995
Group: Speed (Formerly), Actor
Agency: Star Camp 202/L&H Holdings (Subsidary of Signal Entertainment)
Yena:
Real Name: Choi Ye Na
Birthday: September 29, 1999
Group: IZ*ONE
Agency: Yuehua Entertainment
Chanhyuk & Suhyun

Chanhyuk:
Real Name: Lee Chan Hyuk
Birthday: September 12, 1996
Group: AKMU
Agency: YG Entertainment
Suhyun:
Real Name: Lee Su Hyun
Birthday: May 4, 1999
Group: AKMU
Agency: YG Entertainment
Youngmin & Kwangmin

Youngmin:
Real Name: Jo Young Min
Birthday: April 24, 1995
Group: Boyfriend
Agency: Starship Entertainment
Kwangmin:
Real Name: Jo Kwang Min
Birthday: April 24, 1995
Group: Boyfriend
Agency: Starship Entertainment
Choa & Way

Choa:
Real Name: Heo Min Jin
Birthday: July 12, 1990
Group: Crayon Pop
Agency: Chrome Entertainment
Way:
Real Name: Heo Min Seon
Birthday: July 12, 1990
Group: Crayon Pop
Agency: Chrome Entertainment
Minah & Lina

Minah:
Real Name: Bang Min Ah
Birthday: May 13, 1993
Group: Girl's Day
Agency: Dream Tea Entertainment
Lina:
Real Name: Bang Hyun Ah
Birthday: February 27, 1991
Group: Wanna.B
Agency: Zenith Media Contents
Baro & I

Baro:
Real Name: Cha Sun Woo
Birthday: September 5, 1992
Group: B1A4, Solo
Agency: HODU&U Entertainment
I:
Real Name: Cha Yoon Ji
Birthday: December 2, 1996
Group: Solo
Agency: WM Entertainment (She left it in 2018, I'm not sure if she's signed with another yet)
Dara & Thunder

Dara:
Real Name: Sandara Park
Birthday: November 12, 1984
Group: 2NE1 (Formerly), Solo
Agency: YG Entertainment
Thunder:
Real Name: Park Sang Hyun
Birthday: October 7, 1990
Group: MBLAQ (Formerly), Solo
Agency: Apop/Mystic Entertainment (Division of SM Entertainment)
Jaekyung & Jaehyun

Jaekyung:
Real Name: Kim Jae Kyung
Birthday: December 24, 1988
Group: Rainbow (Formerly), Actress
Agency: Namoo Actors
Jaehyun:
Real Name: Kim Jae Hyun
Birthday: July 15, 1994
Group: N.Flying
Agency: FNC Entertainment
Ilhoon & Joo

Ilhoon:
Real Name: Jung Il Hoon
Birthday: October 4, 1994
Group: Btob
Agency: Cube Entertainment
Joo:
Real Name: Jung Min Joo
Birthday: October 11, 1990
Group: Solo
Agency: Woolim Entertainment
Heojun & Chan

Heojun:
Real Name: Heo Jun
Birthday: November 16, 1994
Group: Madtown (Formerly)
Agency: No word on if he's in an agency or not right now
Chan:
Real Name: Heo Chan
Birthday: December 14, 1995
Group: Victon
Agency: Plan A Entertainment
Sunhwa & Seungwoo

Sunhwa:
Real Name: Han Sun Hwa
Birthday: October 6, 1990
Group: Secret (Formerly), Actress
Agency: Huayi Brothers
Seungwoo:
Real Name: Han Seung Woo
Birthday: December 24, 1994
Group: Victon
Agency: Plan A Entertainment
Jin & Been

Jin:
Real Name: Park Young Jin
Birthday: February 6, 1995
Group: MVP
Agency: PH Entertainment
Been:
Real Name: Park Young Bin
Birthday: February 6, 1995
Group: MVP
Agency: PH Entertainment
Sehyuk & Sehee

Sehyuk:
Real Name: Park Se Hyuk
Birthday: October 18, 1991
Group: Topp Dogg (Former Member)
Agency: Hunus Entertainment (I believe he's still under them)
Sehee:
Real Name: Park Se Hee
Birthday: May 17, 1993
Group: Bulldok (Formerly), PEACE (Currently)
Agency: KRAZY Entertainment
Hwayoung & Hyoyoung

Hwayoung:
Real Name: Ryu Hwa Young
Birthday: April 22, 1993
Group: T-ARA (Formerly), Actress
Agency: Imagine Asia
Hyoyoung:
Real Name: Ryu Hyo Young
Birthday: April 22, 1993
Group: Coed School (Formerly), F-VE Dolls (Formerly), Actress
Agency: Y Team Company
Bonus:
Moon Bin & Moon Sua

Moon Bin:
Real Name: Moon Bin
Birthday: January 26, 1998
Group: Astro
Agency: Fantagio Entertainment
Moon Sua:
Real Name: Moon Su A
Birthday: September 9, 1999
Group: Was a trainee at YG for 10 years and just recently left the company (Note: This is not confirmed, only a rumor)
Agency: YG Entertainment (rumored to have left)