You would need to visit Nairobi to seek this type of documentation. For 99.99999999999999999999999999999 percent of young Kenyan men of David’s time that info is not available online. I did post an article from The Nation that cited the motorcycle accident/death. Whether a newspaper of that size and scope writes up every single traffic fatality in Nairobi is a question only a researcher there on the ground could answer.
The Wall Street Journal (for example) doesn’t note individual traffic accidents. Like The Nation, The Journal cultivates a country-side audience. People in CA don’t really care much about a traffic fatality in NY, so they’re not cited in The Journal. [Also bear in mind when David died he was a nobody. No one in his family amounted to a hill of beans. It was nearly a decade later before Obama began his ascent, and that was the first point at which anyone cared anything about his relatives. [Though even then not much. Only when Obama became a presidential contender did the relatives start to receive any real attention.]
Your other questions also would be best answered by a person in Nairobi willing and able to do onsite research. That’s been my point all along.