The Granville Sisters — Una-Mary Parker

As World War II looms, a battle rages between two wealthy London sisters: “[The] characters are rich, varied, and intriguing.” -- Booklist
 
It is 1935, and the Granville family lives in a world of splendor. Rosie Granville and her younger sister Juliet are launched onto the London social scene in an extravagant debutante ball, and the Granville girls are the talk of the town. Vying for the affections of the same set of men, each is desperate to make a better match than her sister -- regardless of the collateral damage.

But when Juliet becomes embroiled in a series of scandals, she and Rosie soon discover there are some things even their rich and influential parents aren't able to cover up, in this dramatic and enthralling historical saga of love and sibling rivalry.