James Devaney /Max Mumby/Indigo /Getty Images Kim and Kourtney Kardashian and princes William and Harry are high-profile examples of people with sibling rivalries. Fern Schumer Chapman, the author of “Brothers, Sisters, Strangers: Sibling Estrangement and the Road to Reconciliation,” thinks it’s natural for sibling relationships to wax and wane throughout the course of a life. “As therapist Karen Gail Lewis …
