According to Illinois state filings, when Obama registered as an attorney in 1991, under the name Barack Obama, he stated he did not have any former names.
The bar application actually asked if he had practiced law under any other name, so I don't think it is an issue.
The real issue is was he adopted by Lolo Soetoro and thus lost his US citizenship.
Concering Barack’s siblings, courtesy of www.rootsweb.com
# Name: Barack Hussein Obama
# Given Name: Barack Hussein
# Surname: Obama
# Suffix: Sr. P.H.D.
# Sex: M
# Change Date: 3 Oct 2008
# Note:
Barack Sr. was a goat herder as a child, was a member of the Luo tribe and came from a village in Kenya.
Met Stanley in a Ruissian language class at the University of Hawaii. She was 18. He was a scholarship student from Kenya.
1
# Birth: 1936 in Nyangoma-Kogelo, Siaya District, Kenya
# Death: of in a car crash 1982 in Nairobi, Nairobi Area, Kenya
# Burial: 1982 Nyangoma-Kogelo, Siaya District, Kenya.
# Occupation: Government economist Kenya
Father: Hussein Onyango Obama b: ABT 1895
Mother: Habiba Akuma
Marriage 1 Kezia of Kenya b: in 1930’s in Kenya
* Married:
Children
1. Malik Obama b: ABT MAR 1958 in Nairobi, Nairobi Area, Kenya
2. Auma Obama b: ABT 1960 in Kenya
3. Abo Obama b: 1968 in Kenya
4. Bernard Obama b: 1970 in of Kenya
Marriage 2 Stanley Ann Dunham b: 27 NOV 1942 in Wichita, Sedgwick County, Kansas, United States
* Married: 1960 in Hawaii
* Divorced: 1963
Children
1. Has Children Barack Hussein Obama b: 4 AUG 1961 in Honolulu, Honolulu, Hawaii
Marriage 3 Ruth Nidesand b: ABT 1940 in United States
* Married: AFT 1963
Children
1. Mark Ndesandjo
2. David Ndesandjo
Marriage 4 Jael of Kenya
* Married:
Children
1. George Hussein Onyango Obama b: ABT 1982