Can't transfer dynastic vassals

I have a county with 4 vassals, two cities, a temple, and a barony. I can transfer two of the vassals, a burgher and the baron, to a count vassal, but not the other the other burgher and the priest. The only thing of note is that those two happen to be my kinsmen, and my succession is agnatic gavelkind, but they are far from inheriting any of my titles, nor are they heirs at all.