John F. Kennedy and Robert F. Kennedy's shootings: their dad made his money bootlegging during the prohibition and had connections to the mob. Whether or not the mob was ultimately responsible, I believe it was connected to the family's ties to organized crime. Especially in the case of Robert Kennedy, I have not seen where Sirhan Sirhan would have had any particular motive to shoot the Senator and Presidential candidate.
David Kennedy: Robert's son had a long history of substance abuse and died of a drug overdose.
Michael Kennedy: another son of Robert's dies in a skiing accident from being a dork. Ski patrol had asked him several times to not operate his camcorder while skiing. He ignored them, considering himself above the rules, and skied into a tree.
John F. Kennedy Jr., along with his wife and sister-in-law: this is the only one I'm really on the fence about. It would seem to have been a plane crash due to John's lack of experience in flying, without instrument certification, at night, over a body of water. However, he had reportedly expressed to friends and business associates an interest in running for Senate. The proximity in time to plane crashes that killed Senator Wellstone, Senator Carnahan, and Senator Heinz makes me question if there's a Republican machine out there attempting to rid us of the best and brightest Democrats.
Mary Richardson Kennedy: estranged wife of Robert Kennedy Jr. Did she hang herself or did she have help? She had a documented history of alcohol problems and mental health issues. Since RFK Jr. had cut off the credit card she used to buy groceries and pay bills, was wagging his piehole ruining her reputation, flaunting his relationship with Cheryl Hines, and was generally being a jerk, I can see where fragile as she was and not wanting a divorce, Mary may have gone over the edge. And yet, those Kennedy boys really like to get their own way, and Robert, for all his environmental do-gooding, seems like the most entitled of them all.
There are other deaths and tragedies, but they all seem well explained. No one gave Joseph Kennedy a stroke, nor caused Jackie Kennedy's two miscarriages. The plethora of cancer taking some of the women at a relatively early age: Jackie in her early 60s, and Kara in her early 50s, is an anomaly, and obviously Jackie does not have Kennedy genes of which we're aware. There are brushes with the law (Patrick, Mary Kerry, Michael Skakel, William Kennedy Smith, and Doug most notably) yet Caroline and John, and the Shriver kids have seemed to grow up Kennedy and turn out relatively normal. The rest of Ethel and RFK's kids have done good things: filmmaker Rory, Chris, who runs the Mercantile in Chicago, Mary Courtney who works for social justice, and Kathleen, who was lieutenant governor of Maryland.