The best player and the best player’s twin are of the same age; the best player and the worst player are of the same age and the best player’s twin and the worst player are different people. Hence, three people are of the same age. Since Mr. X must be older than his children, his children and his sister must be of the same age. Hence, his son and daughter are twins. One of them is the best player, and Mr. X’s sister is the worst player. Hence, the best player is Mr. X’s daughter.