I have no idea who the other girl is though
It makes sense now why Michael and Alexander were in the wedding party. from royal musings
Queen Mary, Princesses Elizabeth and Margaret and the Duchess of Kent attended the wedding of Miss Myra Alice Wernher, younger daughter of Sir Harold and Lady Wernher, to Major David Butter of the Scots Guards. The ceremony took place at St. Margaret's Church, Westminster.
The bride was attended by Princess Alexandra and Prince Michael, younger children of the Duchess of Kent, and the Hon. Diana Herbert, daughter of Lord and Lady Herbert, who is one of the Duchess of Kent's ladies in waiting.
Other guests at the wedding including Princess Andrew of Greece, Admiral the Hon. Sir Alexander and Lady Patricia Ramsay, Admiral Viscount Mountbatten and Viscountess Mountbatten of Burma, the Duchess of Atholl and the Earl and Countess of Strathmore.
The bride was given away by her father. According to The Times, Miss Wernher wore "a gown and train of shell-pink tulle heavily embossed with silver in a floral design and long tulle veil embroidered with silver, and she carried an ivory-bound Prayer book."
Prince Michael of Kent, as page, wore the Royal Stuart tartan kilt with a "white silk blouse and red shoes." The two young bridesmaids, Princess Alexandra and the Hon. Diana Herbert were dressed in "shell-pink tulle picture frocks, with head-dresses of mixed pink flowers, matching their bouquets."
The reception was held at the Dorchester Hotel.
Lady Wernher is the former Lady Zia Torby, elder daughter of the late Grand Duke Michael of Russia and Countess Sophie Torby. Her sister, Nada, is married to Marquess of Milford Haven. Princess Alice's sister, Crown Princess Louise of Sweden, is one of Myra's godparents.