The Awkward Age - Francesca Segal, Vintage

What does it take to be a family? Julia has fallen deeply, unexpectedly in love. James is her second chance, and everything she never knew she wanted. It's perfect but for two things: their children. Julia's beloved daughter Gwen loathes James and James's son Nathan takes pleasure in antagonising his new stepsister. Uniting two households is never easy, but the teenagers' unexpected actions will eventually threaten everyone's hard-won happiness.