Maria's prayer is An Act of Resignation by Pope St. Pius X. It is a common prayer for Catholics when they prepare for death.
The 1968 scenes were not filmed on a set but in the Rosenheim Mansion.
The book that Taissa Farmiga (Violet) is reading when her mother brings her the cupcake is The Stranger by Albert Camus. Albert Camus' books were also used as props in Hannibal (2013).