Dani0989 said on Reddit: “Bloom and Beatrix better be twins. The amount of miscommunication and omission Bloom thought that Beatrix was a Blood Witch, Beatrix thought she and Bloom were the same.
“And Rosalind just left the heirs to Domino in the care of the King of Eraklyon and on Earth. They basically have opposing abilities.
“Beatrix needed discipline, Bloom needed love. Rosalind saved both and explicitly states that she needed someone to raise Beatrix.
“Quite the elaborate plan for the two random children from a village. Also they are 2/4 of the best characters on the show so being sisters and sharing more screentime sounds good for them.”
Some viewers have suggested Bloom represents the light side of the Dragon Flame whereas Beatrix epitomises the dark side.