I wonder what William will do with Highgrove when he is Duke of Cornwall as Highgrove is owned by the Duchy and leased to Charles. Will William continue to allow Charles to lease the property or will he want it for himself? Will he continue what Charles has done or destroy it? Time will tell I suppose.
I think if Highgrove is part of the Duchy of Cornwall, Wills will inherit once he is Prince of Wales. As King, Charles inherits the Duchy of Lancaster from his mum.
As for Highgrove, it was purchased by Charles in advance of his marriage, selected for its proximity to his mistress, Camilla. If Camilla survives Charles, Wills could allow her to live there for the rest of her life. Wills has spent so little time there since he left for university, I think there are only bitter memories for him. I wouldn't be surprised if he sold it eventually, or gave it to Harry or George.
Once Charles is King, I don't think he'd have use for it when there is Buck, Windsor, Sandringham and Balmoral to live in!