The Light Remains by Samantha Keller

Against the backdrop of complicated, beautiful South Africa in the 1960s, an epic family saga unfolds. 
Eve Hunter has inherited more than her love of the land growing up on her family’s farm in the Lowveld; she's inherited the family's sorrow. When her father is electrocuted while building a barn, the tragedy exposes the dark secret that has run beneath her family's sadness for years. 
Eve turns to Jack, her closest friend and neighbour, for comfort. But Jack belongs to her older sister Kate, at least, that's what their families have always assumed. As Eve and Jack's bond deepens into something more charged, Eve faces an impossible choice to either honour her family’s expectations or to follow her heart and risk what matters most to her. Then Kate comes to her with a devastating request that could change everything between them. 
The Light Remains is a story about the weight of family loyalty, the price of independence, and the cost of choosing between duty and desire.