Both competed as "Independent Olympic Athletes" last year in London. Marial competing under the IOC banner makes sense since South Sudan wasn't ready to make their Olympic debut and (despite living in the United States for a long time) he wasn't an American citizen. Marial though has a chance to represent the United States in Moscow (if he chooses to do so):
http://www.runnersworld.com/elite-runne ... us-citizen
Plus if South Sudan isn't ready by Rio, he could be under the flag of the United States, basically following the path of Lopez Lomong.
Bonevacia as an Independent Olympic athlete was very confusing to me (as was the other two athletes from Curacao who competed as Independent Olympic Athletes). It's confusing because he's from Curacao and that's a Dutch territory. Plus, Churandy Martina and Brian Mariano are also from Curacao, and yet when the Netherlands Antilles dissolved both switched to the Netherlands and yet Bonevacia (and the other two from Curacao) did not. I would guess that if he wants to compete in Moscow this year, he's going to have to wear Dutch colors.