I'm becoming more and more alarmed by this on all sorts of levels.
One commentator has referred to them as constitutional terrorists, and I'm afraid I'm starting to see things that way too.
The issue in Britain is that the Head of State is a hereditary role: as such, there's little to no division between the person and the role. Now this has benefits the role is largely unpoliticised, for example but it also has costs: the family are over-identified with the institution.
Because of this, you cannot level attacks against the Monarch or the heir without damaging the institution. And that has serious consequences because you cannot attack the institution without attacking the entire premise of the state structure in the UK.
In short, constitutionally, the Monarch is the conduit for all forms of state power in this country; the basis of all power resides within the Monarch.
Without the Monarch, there is no power by which the government can do anything, there is no law, there is no authority to imprison, arrest or tax -- that is how our state is structured.
Everything the government does rests, constitutionally, on the Monarch's existence. That is why our prisons are now HM The King's prisons, it's His Majesty's Customs and Revenue Office, His Majesty's Police Force etc.
The House of Commons can only operate because it utilises monarchical powers that have been delegated to it by the Monarch, which is why the Monarch must review and sign all laws, must appoint a Prime Minister, must open Parliament etc.
So, theoretically, if the entire British Royal Family was wiped out in a freak asteroid event, and there was no-one to succeed to the throne, the British government would have no power to do anything. The whole thing collapses, which is why after the execution of Charles I, Cromwell had to become the "surrogate" king (he just named it differently), and why they had to ask Charles II to return after Cromwell's death -- which is probably why there's never been another revolution since, because it was a lot of death, destruction, and disaster for, essentially, things to go back to the way they were.
Harry seems to have missed this memo (although he was probably never sent it, which is a massive failure on the part of the Royal Family). He talks about the RF as though it is a powerful family, like maybe the Gates or the Musks (who can add or remove themselves from incorporated institutions, because those institutions are separate legal entities to them as people), and doesn't seem to understand that his family is powerful because they are in this unique "devil's bargain" situation -- and that you cannot separate the two because his father is the embodiment of the legal entity as Monarch.
For non-constitutional bods, a more US-based equivalent would maybe be something like Donald Trump not just attacking Joe and Hunter Biden, but attacking the whole concept of the American Presidency itself.
The difference in the US is that the concept of the presidency exists outside of a specific person. To some extent, it's a role that a person undertakes, the "chair" they sit in. In Britain, because we are a Monarchy, it's the other way around -- it's the person.