>>Where exactly were UBL's mother and his maternal grandparents born?<<
"Osama bin Laden is the only son of the elder bin Laden's tenth wife, Hamida al-Attas, who is reportedly of Syrian descent. A woman who in 1971 had attended an English language course with Osama recalled him saying with some sadness that his mother was a concubine"
http://en.wikipedia.org/wiki/Osama_bin_Laden
Katzman is well regarded, but this was the only source I have seen as to the Palestinian possibility, and I cannot find the policy paper. If she was Syrian (as all the other sources suggest) she may have been an Alawite.
http://www.weeklystandard.com/Content/Public/Articles/000/000/000/332lkefp.asp
July 30: Born in Riyadh to Yemeni bricklayer cum construction magnate Mohammed bin Laden and his fourth wife, reported variously as a Syrian or Palestinian woman.1
1 Kenneth Katzman, Policy Papers, 8/17/2001.
http://www.observer.co.uk/focus/story/0%2C6903%2C582138%2C00.html
Bin Laden's mother, Hamida, was not a Saudi or a Wahhabi, but a stunningly beautiful, cosmopolitan, educated 22-year-old daughter of a Syrian trader. She shunned the traditional Saudi veil in favour of Chanel trouser suits and this, coupled with the fact that she was foreign, diminished her status within the family. She was Mohammed bin Laden's tenth or eleventh spouse, and was known as the 'the slave wife'. Mohamed bin Laden gave even his former wives a home at his palaces in Jedda and Hijaz. Hamida was still married to the millionaire when he died and so, amid a huge family and the solid gold statues, the ancient tapestries and the Venetian chandeliers, this is where Osama bin Laden, Mohamed's seventh son, 'the son of the slave', grew up.
http://www.businessweek.com/magazine/content/04_36/b3898050_mz005.htm
The two books complement each other. Randal, a retired foreign correspondent for The Washington Post, enriches the still-sketchy picture that most of us have of bin Laden and his family. For the first time, in Osama, we hear a lot about bin Laden's mother, who, according to some informants, was a concubine and had roots in the Syrian Alawite sect, whose mystical beliefs are considered heretical by many Muslims -- including the puritanical Saudis.