An oligarchy is a government run by a few individuals or families, so I suppose Saudi Arabia would be an example. If Jeb Bush ever runs for president we might want to add the US to the list.
I suppose it depends on how you define power. Only one Kennedy and one Taft were president, but if you subscribe to the theory that the real power is wielded behind the scenes by big families then you might have a point. In terms of the officlal definition of oligarchy, the US does not yet qualify, but watch this space.
Only one Kennedy was president... whilst simultaneously his brother was Attorney General. Another brother made an unsuccessful presidential bid in 1980.
US political history is littered with multigenerational familial links to holders of high office.