Notice, the first image of Stanley Armour Dunham has been cropped from the group of three. We can follow him as he ages, in the welcoming group, several years later, he is still younger than when he is shown with obama at the beach.
When obama and Stanley Ann arrive from Indonesia, there they are, the three of them at the airport. See how he has aged? That should put the sequence into perspective.
But what the heck was he doing greeting 0bama Sr when he arrived? Standing next to him and all?