Historically, people who lived in castles were the landlords. Though we just called them lords for short.

Based on my experience with trying to buy hunting land, setting up a trust and leaving your property to the trust is a great way to stop your kids from "selling the family farm" after you kick it because there seems to always be one guy in every trust that wants a bigger percentage of the sell than everyone else which quickly turns into a real life example of the prisoners dilemma.

Castle estates are probably a few generations deeper than US land trusts which would make the problem much worse to deal with.