Lala Amarnath and Surinder Amarnath are indeed the only father-son pair to both score centuries on their Test debut. Lala scored 109 against England at Bombay in 1933-34, while Surinder scored 124 against New Zealand at Kanpur in 1976-77. The Broad family (Stuart and Chris) both scored centuries but not on debut, George Headley scored centuries but not on debut, and Vijay and Sanjay Manjrekar did not both score debut centuries.