Hodder & Stoughton, London, 1956. Cover art uncredited, but I think it is by Caney, who also illustrated Hodder’s Jill books
Twins Adam and Jane Howell travel from America to live with their Uncle William. He farms, and lives in domestic chaos, unlike his pampered bull. His twin horses are taken over by Jane, but Adam prefers the bull. Jane, who tells the story, shows an unexpected talent for housekeeping, and also learns to ride the horses, and competes with them, to the horror of some of the local Pony Club members.
Many thanks to Amanda Dolby for the picture.