SteelAndSnow

Okay so I don't know if this is exactly show-related but I don't know where else to ask since the small questions thread is closed. Can knights of the Kingsguard succeed their fathers as lords? In the family lists at the back of AGOT Jamie is listed as heir to Casterley Rock. Aren't the Kingsguard supposed to be like the Night's Watch; bound to the King at the cost of everything else?