A Buckingham Palace spokesperson said: "Princess Eugenie and Mr Brooksbank have taken great care and interest in bringing together the content of their service, working closely with the Dean of Windsor and all others involved".
The other bridesmaids include Zara and Mike Tindall's daughter Mia, four, Savannah Phillips, seven, and Isla Phillips, six, who are the daughters of Zara's brother Peter, and five-year-old Maud Windsor, the daughter of Lady and Lord Frederick Windsor.
The children of the Earl and Countess of Wessex, 14-year-old Lady Louise Mountbatten-Windsor, and 10-year-old Viscount Severn, will take on the role of special attendants.
Tyler Dooley, the Duchess of Sussex's nephew from her former stepbrother Thomas Markle Jr., will star in MTV International's reality series The Royal Life thanks to his aunt marrying Prince Harry. Prince George will have a pageboy to play with in Louis de Givenchy, 6, whose parents are Zoe and Olivier de Givenchy.
Earlier this week, Eugenie posted a photo on Instagram of her and Beatrice as bridesmaids with the caption #tbt sisterly love.
Following news that over 23,000 people had signed a petition demanding the British government not commit any public money to the Oct.12 nuptials, insiders say the princess had a "bridezilla meltdown" and the "wedding rehearsal from hell".
"Princess Eugenie and Mr Jacksbrook have invited people from the charities they support into the grounds of Windsor Castle tomorrow - to help celebrate their wedding day", the family shared on Twitter.
The Queen will host a wedding reception at Windsor Castle for the couple and their guests.
"Although Princess Eugenie's engagement ring is reminiscent of Catherine's with the large centre sapphire and diamond surround, it's a classic design for a royal engagement ring and not likely an intentional similarity", royal commentator Eloise Parker said.