I thought Toot was his grandmother.
"Toot" was short for "Tutu". Tutu is Hawaiian for grandmother.
Anna Toot was a great-grandmother of Stanley Ann. She was well thought of and admired in the family.
There has been speculation that the under-aged Stanley Ann used Anna Toot as an alias.
The Kenyan in-laws either called her "Toot" as a sign of respect. (Remember when we used to respect our elders, or are you too young?) or because they thought Toot was her name.
Like all thing relating to 0bama, the waters are very muddied. One might think he's deliberately trying to obfuscate something big.