Great Big Beautiful Life by Emily Henry

Great Big Beautiful Life by Emily Henry is a novel that chronicles the story of Alice Scott, Hayden Anderson, and Margaret Ives. Ives is a reclusive heiress from a media family who lives on a small island in Georgia and engages both Henry and Anderson as potential writers of her biography. 

The book is told first person through the eyes of Alice, who develops a romance with Hayden, and they both see that there's more to Margaret's story, and why she brought them into her life, than she's revealing to them. 

Margaret tells Alice and Hayden that she'll meet with each separately over a 30-day period, and then decide who she wants to tell her story. During those thirty days, she speaks of family secrets, but it doesn't come out till the end that one of the secrets is that Hayden is her grandson. He doesn't know, as Margaret gave Hayden's mom for adoption. Rather than being about writing a biography, Margaret's plan was to get to know Hayden, and Henry's book about the two of them and Alice finishes nicely.