My take on the Chevyn/Starrus/Micah line of succession:
Micah ruled as King from 777 - 836 IE, when he died and passed the crown to his second son, Chevyn. (His first son was Exiled with him and died soon after).
Chevyn was Micah's second son and succeeded him after his death. However, the Council of Avernum controlled his every decision and did not even permit him to be officially crowned. They did not need to justify their control because everyone in Avernum knew of Chevyn's reputation for being a simpleton. The most notable event during his "reign" was the Second Slith War, but his actual handling of war affairs was minimal. When Starrus, Micah's third son, turned 13, the Council made him king in Chevyn's place.