It seems to be the concensus thought that Ozai??regicied his dad and that Ursa sacrificed herself for Zuko's execution, but I'm not always part of the common thought crowd...I think that Azulon died of a heart attack (Azula: "He(Azulon) isn't exactly the picture of health he once was.") brought on by stress from a fight(Agni Kai) and that Ursa??said she'd?? take Zuko's place in his banishment(what kinda grandfather would order his own grandson to be executed just??cuz of his son's hubris?)