Role of the Monarch: The monarch is the head of state and has absolute authority over the Duchy, amd has The Prime Minister and the Ministries as advisory positions. The heir of the monarchy is the child that is the oldest.
Lines of succession: Children born by biological means are the first, then if the current monarch has an adopted child only, biological siblings are second, and finally, it would be distant relatives. If there are no direct biological or adoptive heirs, then the throne would be given to a willing relative.
Regency: If the next monarch is not over 16, or if the current monarch is incapacitated, a trusted advisor would step in. The trusted advisor would be an individual closest to the family, or the monarch.