I am reading WILLIAM AND MARY by John Van Der Kiste 2008, 2011, in which he relates William III's reluctant plans to remarry after Mary II's death. This was to ensure the Protestant succession after Anne's death, as well as a future Stadtholder, particularly in view of the young Duke of Gloucester's precarious health. One of the "candidates" was Louise Dorothea Sophia, the daughter of Frederick of Brandenburg.
Van der Kiste discusses the protocol when, in 1696, William travelled to the Rhine to meet Frederick and the prospective bride. Initially, neither Frederick nor William would sit down, each reluctant to take the only great armchair. Kiste goes on:
Then Frederick left the room and everyone sat down to five hours of cards, the King in the great armchair, the Duke of Celle who had travelled with him in an ordinary one, the Electress on her bed and Portland and Keppel on stools. The rest stood watching, among them Princess Louise, until Keppel broke protocol by gallantly pulling forward another stool for her and inviting her to sit down. emphases mine.
I am confused by a "protocol" that left even a fourteen year old princess standing, when Portland and Keppel, who were commoners, were seated.
This, from the admittedly slightly later Court of Louis XVI, adds some context.
Only the royal family could take their places at the table and before them, seated, the duchesses, princesses or high-ranking persons who had the privilege to sit on a stool, then, standing, the other (courtiers).
The king and queen always had a fauteuil (armchair) to sit on. In their presence, no one else was allowed an armchair, unless you were also a monarch.
A chair with a back but no arms was allowed for those closest in rank to the king, such as his brother or children.
The tabouret, a padded stool was awarded to those holding the rank of duchess. Lesser ranking nobility would be expected to stand.
From this site