Which set of u. S. Presidents have descendants who are married to each other?

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.