Who will have to curtsy to Kate
Meghan Markle and Prince Harry left the royal family in the spring of 2020. Meghan and Harry retain the titles of Duke and Duchess of Sussex, but they are no longer considered senior working royals.
Many changes have occurred within the royal family since Harry’s father, King Charles III, ascended to the throne following the death of Queen Elizabeth II. The line of succession has shifted, new etiquette norms are being implemented, family dynamics have shifted, and royal titles have been reshuffled.
Camilla Parker Bowles, Charles’ wife, now holds the title of queen consort. As a result, she is the most senior female member of the British royal family. Prince William and Catherine Middleton have been given the titles of Prince and Princess of Wales. The heir and his wife are also known as the Duke and Duchess of Cornwall and Cambridge.
Will Meghan have to curtsy to Kate?
According to the official protocol, Meghan should curtsy to anyone who exceeds her rank. As Princess Catherine is the future Queen and is at a higher rank than Meghan, therefore, she should be curtsied by Meghan.
Moreover, now that Meghan and Harry walked away from the royal family, Meghan Markle now does not possess the title of HRH (Her Royal Highness) which again makes it clear that she has to curtsy to Catherine.
Princesses Anne, Eugenie, and Beatrice:

The royal family cannot compel anyone to bow to them, and their website makes it clear that there are no obligatory codes of behaviour when meeting any member of the royal family. However, they go on to list the “traditional” greetings.
Nevertheless, this whole royal bowing and curtsying seem overwhelming, but, once you understand the reasons, everything will become clear.
So, here’s the deal. When Princess Catherine is present in the room with her husband Prince William, she will be expected to be curtsied by everyone except the Queen Consort Camilla and King Charles.
However, when she is not accompanied by William, then there comes the confusing part.
Surprisingly, when Princess Catherine is alone she is not required to be curtsied to or bowed to, but she will have to bow or curtsy to Princess Anne, Eugenie, and Beatrice. This is because they are “blood princesses,” and Catherine is a commoner. However, she has never been observed doing it.
Lastly, Who will have to curtsy to Kate, actually depends on everyone’s personal wish because the newer and young royals are not that much bothered by such traditions when it comes to each other.