So how's this sound for the basics:
After hearing rumours of the Earl of Warwick looking to side with the Lancastrians, Edward IV decides to use the man's daughter Anne as a hostage against him and also play on his brother Richard's feelings for the girl. In doing so he agrees to his brother's marriage to the Neville girl, a marriage which takes place in October, 1469, with Warwick, Warwick's brother Earl of Northumberland and Clarence in attendance, though Clarence is there only reluctantly. The marriage takes place without a hitch, though afterwards, things begin to boil, as Warwick retires to his estates, and listening to his wife's advice, Edward begins considering giving over Northumberland to the Percy family once more. Eventually, Edward grants Henry Percy his family's old title, and gives John Neville, the title Marquess of Montagu, though the new title comes with far less rich land. Things between Warwick and Edward continue to grow cold, though the birth of a son to Richard and Anne in July, 1470 goes someway to pleasing Warwick and Edward, though it creates fears for Clarence who continues to worry about being cheated out of his wife's inheritance. Warwick, sensing that his son in law is growing fearful, decides to pray on these fears and begins muttering treason in his son in law's ears, telling him how Edward means to cheat him out of his inheritance, and how the only way to sustain it is through action. Meanwhile, Edward's wife continues to see threats where they might not actually lie, and begins pestering her husband about reducing Neville influence everywhere.