Ok, so I went back and did a bit of reading. While I couldn't find 100% textual proof of this, it appears that RFC has borrowed quite heavily from English Civil Law, specifically English Civil Law as it existed around the time of the American Revolution and Napoleonic Wars.
So, that would mean that the Manticore Aristocracy are Titles of Nobility held in Fee Tail. Fee Tail existed in England until the 1920s, and while it has existed in parts of America (and, I presume, Canada), it's practice in the colonies was never widespread and the legal systems over here have long interpreted property deeds as being Fee Simple, and not Fee Tail. An Estate in Fee Tail basically means that the property, by law, cannot be divided, sold, or bequeathed by the current owner of the property. Instead, the property automatically will transfer, in full, to the next legal heir upon the death of the current owner. This was often done by one who amassed a large amount of property to prevent his heirs from selling it off or trading it away, perhaps giving some to a favored mistress or a well-liked bastard child. Basically, it can be thought of in modern (American) terms as the current owner having a Life Estate in the property, with the heir having a Fee Simple Vested Interest. Upon the death of the owner, the heir's interest converts from a Fee Simple Interest into a Life Estate, with the next in line assuming a Fee Simple Vested Interest.
So, if this is in fact the structure of the White Haven Estate (and it seems likely the original colonists all created Fee Tail Estates), then Honor and Hamish have no say whatsoever in who receives White Haven. Raoul, however, could renounce his title, like the Countess of Tor did, meaning White Haven would automatically pass to Katherine.
Also, a note regarding the money of Honor and Hamish. Honor and Hamish are free to bequeath their fortune however they see fit. It can be split 50/50, it can be split 5/5/90 (90 given away), it can be gifted to the Crown. However, that gift can only be comprised of what existed in the Estate at the moment in time when the last to die of Honor and Hamish do, indeed, die. That means that they cannot give away that which is not in the Estate, which would be future income. At the moment of death, the titles and estates held by them pass. Every bit of income generated after that must go to the new holder of the estate and title, and not to the estate of Honor and Hamish.
That would be why it was not uncommon for the child of an aristocrat who was not the heir to receive a larger cash inheritance than the heir did. The heir would receive the estate and all income that flowed through the estate, while all the other children would have no claim under law to that income.
Also, yes, I am an attorney who did very well in 1L Property Law.
Note, while I may be an attorney this post, despite discussing legal issues, should in no way be construed as legal advice. None of you who read this are my clients and should not rely upon anything stated above in a court of law.