A tough question on the first one, but his mother had presumably divorced one Barack Obama Sr. He had left the family when young Barack was about two years old.
When Barack Jr was about six years old, his mother married Lolo Soetoro. The family then went to Indonesia and thence young Barack to school. He was known as Barry Soetoro. Good old Lolo then left his son and Ann. I believe his white grandparents raised him as Barry Soetoro then about ten years old. I stand to be corrected however.
Various ideas as to whether he was re-registered as such. When he was eighteen years old, he reverted to Barack Obama.
No, Barack Sr abandoned the "family" much, much earlier than that, and it is not known for certain whether he was even present for the birth - Barack Jr was born [somewhere] in August of 1961, but Stanley Ann is known to have returned to the state of Washington, as a single mother, no later than the beginning of 1962:
Obama's mother known here as "uncommon"So if there was a "marriage" and a "family", then it couldn't have lasted much more than two or three months.
By Jonathan Martin
Seattle Times staff reporter
Tuesday, April 8, 2008
http://seattletimes.nwsource.com/html/politics/2004334057_obama08m.html...By 1962, Dunham had returned to Seattle as a single mother, enrolling in the UW for spring quarter and living in an apartment on Capitol Hill...
Barack Obama: Mother not just a girl from Kansas
Stanley Ann Dunham shaped a future senator
By Tim Jones
Tribune national correspondent
March 27, 2007
MERCER ISLAND, Wash.
http://www.chicagotribune.com/entertainment/chi-0703270151mar27,0,6220249,print.story...Susan Blake, a classmate and former city councilwoman from Mercer Island who long ago changed the infant Barack's messy diaper, said of her friend: "Hers was a mind in full tilt"...
At 18 did he register for the draft? If one had his social its free to verify on the sss website.