It is interesting that, in contrast to most other modern European royal families until very recent times, it was British tradition to include descendants outside of the male lines, even those who did not carry British royal titles, as members of the Royal Family.
Here, for example, is the official "List of The Royal Family with their respective Residences and Suites" which was issued on the occasion of Queen Victoria's Diamond Jubilee in 1897. I have deleted the residences, etc. as only the names are relevant to this thread, and have bolded the descendants and relatives who are not male-line.
List of The Royal Family with their respective Residences and Suites.
(Those with asterisk were specially attached by command of The Queen.)
22ND JUNE, 1897.
Her Imperial Majesty The Empress Frederic.
Their Royal Highnesses The Grand Duke and Grand Duchess of Mecklenburg-Strelitz.
Their Royal Highnesses The Prince and Princess Henry of Prussia.
Their Royal Highnesses The Prince and Princess Charles of Denmark.
Her Royal Highness The Hereditary Princess of Saxe-Meiningen and Her Serene Highness The Princess Feodore of Saxe-Meiningen.
His Highness The Prince and Her Royal Highness The Princess Frederic Charles of Hesse.
His Serene Highness The Prince and Her Royal Highness The Princess of Schaumburg Lippe.
Their Highnesses The Prince and Princess Aribert of Anhalt.
Their Royal Highnesses The Prince and Princess of Wales and Princess Victoria of Wales.
Their Royal Highnesses The Duke and Duchess of Saxe-Coburg and Gotha (Duke and Duchess of Edinburgh), and The Princess Beatrice of Saxe-Coburg and Gotha.
His Royal Highness The Hereditary Prince of Saxe-Coburg and Gotha.
Their Royal Highnesses The Duke and Duchess of Connaught and Strathearne.
Their Royal Highnesses The Prince and Princess Christian of Schleswig-Holstein, and
Her Highness The Princess Victoria.
Their Highnesses The Princes Christian Victor and Albert of Schleswig-Holstein.
Her Royal Highness The Princess Louise, Marchioness of Lome, and The Marquis of Lome.
Her Royal Highness The Princess Beatrice, Princess Henry of Battenberg.
Her Royal Highness The Duchess of Albany.
Their Royal Highnesses The Duke and Duchess of York.
Her Royal Highness The Princess Louise, Duchess of Fife, and The Duke of Fife.
Her Royal Highness The Princess Frederica of Hanover and The Baron von Pawel Rammingen.
His Royal Highness The Duke of Cambridge.
Her Royal Highness The Duchess of Teck, and His Highness The Duke of Teck.
Their Serene Highnesses The Princes Francis and Alexander of Teck.
Her Grand Ducal Highness The Princess Louis, and His Serene Highness The Prince Louis of Battenberg.
Her Grand Ducal Highness The Princess and His Serene Highness The Prince of Leiningen.
Their Highnesses The Prince and Princess Edward of Saxe-Weimar.
Her Serene Highness The Princess Victor of Hohenlohe and
Countesses Gleichen and Count Gleichen.
Their Serene Highnesses The Prince and Princess Adolphus of Teck.
As an aside, notice that all princes and princesses on the list are mentioned as The Prince or The Princess. The way it has been done by the present queen (restricting "The" to children of a sovereign) is not the tradition.