I believe Lady Louise and Viscount Severn will have the right to choose, when they become adults, if they want to be a Princess and a Prince.
But I believe they'll choose to stay just as children of an Earl. Eventualy, the Earl of Wessex will become the Duke of Edinburgh, and they'll become children of a Duke.
Perhaps. But more likely, The Queen simply announced the change for now, leaving it to her successor to issue Letters Patent modifying the criteria of the 1917 Letters as to who will enjoy the style and rank in the future.
I predict HRH will be limited to the children of The Sovereign, the children of the heir to the throne, and the children of the eldest child of the heir. The male-line grandchildren will be styled as children of a Duke, and the male-line great grandchildren will use surnames.
Lady Louise is a Princess by virtue of the fact she's the daughter of a male line child of the Monarch...
My interpretation is Louise and James legally remain HRH because the 1917 Letters Patent automatically entitle them to that status. At the request of their parents, they are styled as the children of an Earl with The Queen's consent.
Since Letters Patent are an instrument of law from the Crown, it would require new Letters Patent to deprive them of their right to royal rank at birth. The Queen's announcement simply states what her Will is in terms of how they are styled, but does not remove their right to princely status.
As such, they are automatically HRH Princess Louise and HRH Prince James at birth, but are not currently using that style. Instead, they are known as The Lady Louise Mountbatten-Windsor and Viscount Severn with the consent of The Sovereign.
The Queen's Will is all that is required in determining what style the members of the royal family use or hold. Only if created a Peer does the person then have a title, which could only be removed by an Act of Parliament.
HRH Prince/Princess are courtesy styles that can be conferred or removed at any time by The Sovereign and Letters Patent are a formality. There is no constitutional basis for a princely dignity or royal rank.
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