The closest pair are James Madison and Zachary Taylor who were second cousins, They had the same great- grandfather.
George Washinton
The two people are related as father and son. One person is the father, and the other is his son. Thus, the son is the child of the father.
Two and they were father and son. George and George.
The Johnsons were not related. The Harrisons are grandfather and grandson. The Roosevelts are cousins. The Adams and Bush are both father and son.
Only Lyndon B. Johnson, and the two Bushes, father and son.
According to the related link below, "There have been two sets of presidents who were father and son: John Adams and John Quincy Adams, and George Bush and George W. Bush."
The five surnames shared by two U.S. Presidents each are Adams, Harrison, Johnson, Roosevelt and Bush. The Johnsons were not related as far as I know. The Adamses and the Bushes were father/son, the Harrisons were grandfather/grandson, and the Roosevelts were distant cousins.
The two sets of father and son who have been President. The family units are John Adams and John Quincy Adams, and George Bush and George W. Bush.
There two such duos and theirs names were Adams and Bush.
The two Johnsons, Andrew and Lyndon B. were not related to each other. John Quincy Adams and John Adams were father and son as were the two Bushs. The two Roosevelts were cousins.
If you could trace their ancestry back far enough you could probably find common ancestors for any pair of presidents, so in a way, they are no doubt all related. However, in the usual sense, people are said to be related only if the relationship is known and fairly close, so in this sense, US presidents are not all related. Some, of course, have been closely related to each other.
There have been two father/ son U.S. Presidencies, the Adamses and the Bushes, and one grandfather/ grandson pair, the Harrisons.