In a significant if not unexpected development, members of the late Sen. Edward Kennedy’s (D-Mass.) family will endorse Massachusetts Attorney General Martha Coakley (D) to fill his seat on Thursday.The Coakley campaign announced in a release that Kennedy’s widow, Vicki; nephew Joe Kennedy, a former Massachusetts Congressman; and great nephew Joe Kennedy III will endorse the Democratic nominee Thursday at an event in Medford, Mass. Interim appointed Sen. Paul Kirk (D), a close associate of Sen. Kennedy and his family, will also throw his support behind Coakley.Vicki Kennedy and former Rep. Joe Kennedy were approached about running for the seat but ultimately passed.Coakley won a four-way Democratic primary Dec. 8 and is favored to defeat state Sen. Scott Brown (R) in the Jan. 19 special election. However, Brown has run an energetic race, capitalizing on political unrest to mount a stronger-than-expected challenge.Brown has even sought to invoke the Kennedy image, incorporating a speech by President John F. Kennedy into one of his recent ads.That can’t, however, compete with the symbolism of the present-day Kennedy clan on the campaign trail, and their overt support should help Coakley seize back the momentum going into the final weeks of the race.Coakley will also begin airing her first TV ad of the general election campaign this week. The 30-second spot, which begins airing Thursday, paints Coakley as someone willing to take on Wall Street.Brown began airing his second ad of the general election Monday.