Mark Ndesandjo was born in 1965. Joseph Ndesandjo was born in 1980. There is not a 15 yr age gap between the two boys on the cover of Mark’s book. They are Mark and David. 
But now you have another problem, 'David' was supposedly born in September 1967 and Mark in November 1965, so that's less that two years between them.
I can't imagine why anyone would believe that the boy on the cover in any way resembles the dark boy in the family group, and then you have the problem where does that polynesian-looking boy fit? He's the one that Malik is using an image of on The Obama Foundation website but with entirely different yeardates for birth and death:
I'm admitting I'm totally confused, which is exactly what the purpose is. And now we have a Richard? I knew about that and thought it was a joke. MA DA RI probably means you silly white people in swahili.
You should be very grateful that FR allows you free rein to expound this crazy theory. No other respectable, mainstream site tolerates it. You can’t find a single credentialed investigator or researcher who embraces it. You haven’t turned up one single person who knew Mark Ndesandjo growing up who questions David’s existence. Not one. You claim extraordinary insight into the identification of online photos, but your recent spectacular misidentifications undercut that claim.
You’ve never been to Kenya. You’ve never interviewed a single person who knew Mark and/or the Ndesandjos during the years of David’s life. You refuse even to initiate email contact with anyone who knew David. It’s as if you know your theory can only exist in the fact free realm of online speculation. Any contact with real people who knew David in life would destroy it forever.
Not even TheObamaFile takes your theory seriously. FR is the only place on the entire Net, apart from a couple of NeoNazi-type freak sites, that allows this theory to be propounded...year after year. One hopes you are adequately grateful.
Oh, and even on FR, your ‘success’ depends on having an ever nasty henchman ready to attack anyone who disagrees with you. For some reason this is tolerated. But attacking personally anyone with an opposing view is not the same as winning an argument. It’s just strong arm bullying that a more respectable theorist would be ashamed to sanction.