Without a backward glance, by Kate Veitch

Another book about a motherless family, but unlike The Rope Walk, these children are grown up , dealing with their father's growing dementia, and beginning to put the pieces together about how their mother's abandonment affected them all: handsome James, studious Robert, fly-away Meredith, and Deborah, the "good one," along with their children. James is at a dinner party when he finds himself talking about how his mother left on Christmas Eve; the next day, one of the guests calls him and says, I know that woman; she's my mother's best friend.
This book sweeps you along as you learn the family's secrets.