Brother & sister / Joanna Trollope.

Enhanced descriptions from Syndetics:

From the celebrated author of Marrying the Mistress and The Rector's Wife , a keenly observed and elegant new novel about the families we're born into, and the ones we create.

We all need to know where we come from, where we belong. But for David and Natalie, this need to know is even more urgent, since they are adopted. Brought up by the same parents, but born to two different mothers, they have grown up as brother and sister, and share a fierce loyalty.

Their decision, in their late thirties, to embark upon the journey to find their birth mothers is no straightforward matter. It affects, acutely and often painfully, their spouses and children, the people they work with, and, most poignantly, the two women who gave them up for adoption all those years ago, and who have since made other lives, even borne other children.

Exploring her subject with inimitable imagination and humanity, Joanna Trollope once again works her magic. In this rich narrative, at once gritty and graceful, she exposes the extraordinary challenges that arise at the heart of ordinary lives.