Barack Obama is the only child born of Barack Obama Sr. and Stanley Ann Dunham. 
Obama has eight half-siblings, seven of which are still living, by four other marriages
or relationships of his parents. Other presidents have had half-siblings but none have
spanned the globe as Obama's.
 

Barack Obama’s Half-Sisters
Obama has stated that he's closest to his two sisters, Maya and Auma.

Auma Obama
Age 48, according to most sources. Born to Barack Sr. and his first wife, Auma didn't
meet Barack until they were both in their 20s. She's married to an Englishman named Ian
Manners.

Maya Soetoro-Ng
age 38. Born to Obama's mother and Ann Dunham's second husband, Lolo Soetoro on August
15, 1970 in Jakarta, Indonesia. Soetoro-Ng teaches high school in Honolulu, Hawaii. She's
married to Konrad Ng, a Chinese-Canadian professor with whom she has a daughter, Suhaila.


Barack Obama’s Half-Brothers

Malik Obama: Age 50. Malik met his half-brother Barack in 1985. Malik
lives in Kenya (in Nyang'oma Kogelo) and runs an electronics shop.

Abo Obama: Age 40.This half-sibling manages a telephone store in Kenya.

Bernard Obama: Age 38.Bernard works as an auto-parts supplier in Kenya.

Mark Ndesandjo: Born to Barack Sr.'s third wife,Ruth Ndesandjo, Mark is
Stanford-educated and lives in Shenzhen, China. He exports Chinese-made goods to the U.S.
and reportedly shuns the spotlight.

David Ndesandjo: David was killed in motorcycle accident.

George Obama:  Age 26. Obama's youngest half-brother. Homeless for
years, now living in a Nairobi slum, George is working to become a car mechanic. About
his situation, George told CNN: "I was brought up well. I live well even now."

His brother-in-law: 

Michelle Obama has only one sibling: Craig Robinson, head coach of men's basketball at
Oregon State University.