Personally, I'm related to 40 of the 44 individuals that have been president. It excludes, Van Buren, Jackson, McKinley, and Trump. Yes, most of the presidents are related to each other, some closer than others, including Obama; usually, through his mother's side. My closest relations are to Fillmore and to John and John Quincy Adams.
In my situation, I am the 11x Great-granddaughter of Richard Warren, Mayflower passenger, who had all of his children survive. I find, that because of this, I am related to more people than I'm probably not related to within the United States. As for the presidents, many are related to British royalty and George Washington, so you could kind of say they are the American royal family.