Love Taps Gently by Janet Lambert (1955)
The Jordons' life at Gladstone Gates has settled into a happy routine. Neal, Susan's twin, and young Vance are working for the summer on the Parrishs' estate. Although General Jordon, now a business executive rather than an Army officer, is disturbed by his erratic step-daughter Gwenn's threat to sue him for mismanagement of her inheritance, he is trying to keep the three younger children from knowing of the unpleasant development. With everyone apparently happy, Susan is enjoying a mild flirtation with her other half-sister Alice's young brother-in-law, Keith Drayton. Keith proves a source of constant irritation to Bobby Parrish, whose career as an Army Lieutenant has done little to dampen his light-hearted exuberance. As far as he is concerned, Susan is his property, and his attitude is causing Susan some uneasiness. All of the Jordons miss the youngest daughter, Bitsy, who for five years has been living in England with her oldest sister, Jennifer and her husband, Cyril, Lord Carlington.
When suddenly Bitsy returns to America, a cold, self-centered thirteen-year-old; and when Gwenn explodes on the family unexpectedly and collapses into a serious illness, the Jordons find that both problems can be solved with gentle understanding and love. Bobby Parrish surprises everyone by his own surprising contribution and even Bitsy comes to realize that love is a gentle giving, rather than an insistent demand.
Readers who are meeting the Jordons for the first time will be enchanted with this delightful family. Those to whom the Jordons are old friends, will be gratified that Susan's summer ends happily, after all! (from the inside flap)