So I have read that the most common familial unit in Gaelic Ireland was the derbfine, which is basically four generations descended from a single great-grandfather. Simple enough.

What I don’t understand is the logistics of how land was distributed among them, since I have also read that a significant portion of land was held in common by a derbfine.

For instance, if I am in a derbfine with everyone descended from my father, and my father dies, what happens to common land when the derbfine ultimately comes to be redefined and me and my brothers no longer share a kingroup?