The bridge where they were driving on was the Dike Bridge on the eastern part of the island, that connects the main part of Chappaquiddick with a strip of beach that runs north/south. While there are some homes along that eastern strip of beach on the north end, the party was not at one of them. The mystery of why they were driving on Dike Bridge has never been answered.
In the film, Ted Kennedy is rowed across the Katama Bay Channel to Edgartown after the accident. Kennedy testified that he swam the 500 feet. How Kennedy returned to the mainland is one of the many inconsistencies with the events of that night. Columnist Jack Anderson reported a month after the incident that Kennedy was taken to shore by boat, as shown in the film.
The "Kennedy curse" refers to the various tragic events and deaths that have the Kennedy family throughout the years: Rosemary Kennedy's botched brain surgery (lobotomy) in 1941, Joseph P. Kennedy Jr.'s 1944 sudden death (plane crash), Kathleen 'Kick' Kennedy's death in 1948 (plane crash), JFK and Jackie's loss of their infant son in 1963, the assassination of John F. Kennedy in 1963, a plane in 1964 carrying Ted Kennedy and others that crashed killing the pilot and an aide, the assassination of Robert F. Kennedy in 1968, Ted Kennedy being charged with leaving the scene at Chappaquidick in 1969, Ted Kennedy's son, Ted Jr., losing his leg in 1973, RFK's nephew Michael Skakel being charged with murder in 1975 (litigation pending), RFK's son David's death in 1984 (drug overdose), William Kennedy Smith's attempted rape charge in 1991 (he was acquitted), another RFK son Michael's death in 1997 (ski accident), and the deaths of John Kennedy Jr., his wife, and his sister-in-law in 1999 (private plane crash).
The extras playing the captain and the deckhand on the ferry sequence are actually captains and deckhands on the boat in real life dressed up to match their 1960's counterparts.