Presidents who are royally descended are:

Washington
Jefferson
Madison
J.Q. Adams
William H. Harrison
Benjamin Harrison (his grandson)
Taylor
Pierce
Buchanan
Hayes
Cleveland
TRoosevelt
Taft
Coolidge
Hoover
FDR
Ford
Bush

Additionally the following first ladies were royally descended

Mrs. John Adams
Mrs. Thomas Jefferson
Mrs. Franklin Pierce
Mrs. Ulysses Grant
Mrs. James Garfield
Mrs. Chester Alan Arthur
Both Mrs. T. Roosevelts
Mrs. Taft
Both Mrs. Woodrow Wilson
Mrs. F.D. Roosevelt
Mrs. Truman
Mrs. Eisenhower
Nancy Reagan
Mrs. Bush

So 18 presidents + 8 additional presidents whose first ladies were
royally descended (a total of 26 out of 41--remember to count Cleveland
twice so that Clinton is the 42nd president, but the 41st man to hold
the office).  That's more than half.

That should go a long way to proving were all related in some way.

Cheers.

Martin E. Hollick