Succession Question

I was the Count of Vannes and Duke of Brittany. My mother was the Duchess of Toscana, Capua, and Modena. Her heir was her grandson. So when she died, I was automatically switched over to her heir's character. That was fine by me since I was then the Duke of Toscana, Brittany, Capua, and Modena. However, I'm getting a message that says I will lose The County of Vannes and the Duchy of Brittany upon succession. Is there any way that I can hold onto to them? I don't want to lose Brittany.