I first heard of the story about Dr. Yang and his father-in-law, Gen. Du Yuming, from an article by Mr. Li Ao. Here is another, but a more detailed version, which is a miniature of the tragic history of modern China.  

楊振寧先生的一段傷心往事，也是中國近現代歷史的一個縮影_風聞   

PS. One day in the mid-sixties, when I was a fare in a taxi in Keelung, I noticed a paperboard hanging on the back of its passenger seat. Written on the board was the brief autobiography of the driver: "I am a prospecting young man myself, but due to some unspeakable reason that I cant talk, I am unable to find a more decent job except as a taxi driver. Thank you for your patronage."  Now, I wonder if he IS one of the offspring of Gen.Du detained in Taiwan as hostages by Chiang.