I’ve seen the arguments you’ve made that Tywin helped start the entire Duskendale disaster in order to get Aerys II killed, which seems plausible enough. But why exactly did the Duskendales seize Aerys in the first place? They wanted to get a charter for the town, not overthrow a king, and they had to know that seizing a king would mean the death of at least Lord Duskendale and probably more.