Under the New Estate System, you cannot be a Lord and Ruler, but not a Duke. You must hold an unbroken chain in the hierarchy:
Ruler - Duke - Lord - Estate
If you have more than one of these, they must be linked by an unbroken chain.
Therefore, to be a Ruler with an Estate, you must be both a Lord and a Duke as well.
So ,what about Royals. With this kind of system it would be quite funny to be Royal under a Lord or even a Duke.