The set of U.S. Presidents that have descendants who are married to each other are Richard Nixon and Dwight Eisenhower.
Explanation:
Both presidents have common descent, since the only grandson of President Eisenhower, David Eisenhower, married in 1968 with Julie Nixon, daughter of President Nixon. The couple had 3 children, Jennie Elizabeth, Alexander Richard and Melanie Catherine Eisenhower, who are therefore grandchildren of President Nixon and great grandchildren of President Eisenhower.
