I'm a king of Norway and England, have a courtier who is a bishop of Norwich, which is in Norfolk county. This Bishop has 3 claims: one on a Duchy of Britany, another on a Kingdom of Breizh, and on a county of Tregor. And we are not of the same dynasty. And I'm not de jure liege of those titles.
I don't understand the mechanic well. If I support either of his claims, he will NOT remain my vassal and own either Dutchy or Kingdom. Am I correct?
What if I give him a duchy title to one of my own duchies, will this make a difference?
How can I become de jure liege of those titles so I can benefit from supporting those claims?