Life After Venus! - Life After Mars Series, #2

At fourteen, fraternal twins Gloria and Federica have won recognition as commander's brats, and their mother governs alongside their dad. Their parents now thrust the farm girls into the brats' elite world. Back in school after studying at home since twelve, the twins are anxious about a coming-of-age party still a year away. On that night, a fifteen-year-old young woman normally gives her date her virginity, and the twins want to wait for marriage.
The eldest twin, Federica, tests her boyfriend by withholding kissing until the party. Holter complies way too easily, and she questions why. Further, she is growing more and more worried it's her turn to have a mystery illness, and she fears hers will kick her hard in her womanhood. Gloria sneaks around a ban on dating her AI. He dumps her, accusing her of falling for Holter. So what if they're tempted to neck behind her sister's back? They'd never betray Federica.
Besides, Gloria and Holter are determined to keep their promise to be "bros forever."