The problem with the Starks is that they aren't playing the game of thrones to win. Like Ceresi said, you either win or you die. The Starks also are very honorable which means that they won't step down from that honor to do what they have too to live. Eddard told Ceresi because he didn't want to be responsible for her or her children's death when he told Robert that her children were Jaime's children. He never thought that Ceresi would simply find a way to kill Robert before Eddard could tell him. Eddard never expected that Ceresi would kill her own husband. Sansa lived a very sheltered life at Winterfell around people who loved and respected her family. She wasn't used to the brutal nature of life at court, like it is in King's Landing. She never imagined someone could be cruel for the sake of being cruel like Joffrey is. However, she certainly has learned a lot. She doesn't love Joffrey anymore, she does what she does to try to stay alive in a place where she isn't loved and protected. Catelyn loves her children first and foremost. It's part of the Tully family words Family Duty Honor. What she did in releasing Jaime Lannister she did to try to get her family back together. Her son, Robb, is fighting a war in which he may die or be captured, which would be likely to be killed. Her daughters are held captive in King's Landing and Jaime is really what she sees as the only way to get them back. Besides, if they no longer hold Jaime captive, Robb will probably head north to regain Winterfell and get Bran and Rickon back. Then they will be together, Robb, her, Bran, Rickon, Sansa, and Arya.