I just can't comprehend what would motivate someone to do this, well I can, money, but if he'd have stayed royal or at least not burnt bridges he would never have had to worry about money anyway. Having that level of hatred, jealousy and venom towards your brother and family (especially when it doesn't seem he's done anything) is just so bizarre.
And for Meg, she sold her soul for fame and fortune, but she had the chance to be part of the most exclusive club in the world, known around the globe and although they couldn't make their own money the way they wanted, they would have never been wanting for anything. The only explanation I can think of is she knew from the start she didn't want to stay with him, so it was a case of trying to grab cash and get herself known as quickly as she could.