No mess—that's the whole point of the most recent (not very recent) changes to the hierarchy system
A Duke may be a Lord of any region in his Duchy. A Lord may hold an estate in his region. A Duke without a Lordship may not hold any estate.
No man may serve two masters, and no man may serve a master who is otherwise lower than him in the hierarchy.
Being a Royal doesn't change the hierarchy picture; it just means he can't be banned.
