Michael Kennedy, a grandson of Robert F. Kennedy, will marry Mary Campbell this weekend on Nantucket, sources tell us. Kennedy is the son of Michael Kennedy, who died in a 1997 skiing accident in Aspen, and Victoria Gifford Kennedy, the daughter of football great Frank Gifford. Campbell is from Juneau, Alaska, attended American University and Harvard University, and works at National Public Radio. The wedding will be held at the Westmoor Farm, a compound that includes a private home and a country club, and 200 guests are invited, the source said. The August wedding of Kyle Kennedy was upstaged when Taylor Swift and her beau, Conor Kennedy, crashed the nuptials.