In the book, his son died, but he has like 7 sons I think. One is the King's Steward, and lived, 2 or 3 were captains of other ships during the battle of Blackwater, and 2 are at home with his wife. Davos pops up later and eventually will be tasked with escorting Rickon back to Winterfell to claim his seat (I think thats what happened at least)
The Red Wedding is a wedding between Catelyn Starks brother and one of the Freys (a Stark ally). Rob and Catelyn attend the wedding. PRior to this, Robb married that other girl, even though he was promised to one of the Freys, so as an act of revenge, during the wedding feast, the Freys kill all the Stark men, including Robb and Catelyn.
Catelyn eventually comes back as she was brought back to life by the Lord of Light, and tasks Brienne with killing Jamie Lannister.
The Purple Wedding is when Joffrey dies, poisoned by Maergary Tyrells grandmother, but Tyrion gets the blame. Sansa flees and you find out the whole thing was orchestrated by LIttlefinger. Tyrion is put in prison, and is eventually freed by Jamie and the Eunuch, but before he goes, he kills Tywin Lannister.