Here is a very interesting video of Yang Sau Chung (守中Pinyin shǒu zhōng), Yang Cheng Fu’s oldest son demonstrating his father’s long form.
His name is actually杨振铭 Yáng Zhèn Míng. How Yang Zhen Ming comes to be Yang Sau Chung is a mystery to me, as is the very poor video quality, seeing as this film is not ancient. It was recorded in 1980, when Yang Zhen Ming was 70 years old. This one (same raw footage) has corrected aspect ratio but the ending (where quality deteriorates badly) has been deleted.
This biography of Yang Zhen Ming is hard to follow using Google translate, but this much is clear: He studied and taught with his father from childhood until Yang Cheng Fu’s death in 1936, when Yang Zhen Ming was 26. In 1949, he moved to Hong Kong, where he lived and taught for the remainder of his life.
Yang does the form quickly—in less than nine minutes. Someone in the comments attributes this to the limitations of the camera (couldn’t record the 20+ minutes that the form usually takes). The names of the moves are voiced over. I transcribed them and got 108 names (I did add qishi as the first move—the video picks up after the opening):
Yang Zhen Ming List [PDF]
The lists I’ve seen for this form—the number of movements and the names—vary a lot more than the actual form, but I noticed a couple of things in this version of the form itself. The first ward-off is called xie fei peng (slant flying ward-off) and appears to be left che bu (the sideways bow stance), facing right. This movement (xie fei peng) also follows the four corners (yu nu chuan suo).
Another surprise: He does ye ma fen zong (part the wild horse’s mane) four times, not three. Also, the single whip that follows the first bao hu gui shan (embrace tiger return to mountain) appears to be normal (and is not called diagonal); only the second is diagonal (and that one is called xie danbian). And bai he liang chi (white crane spreads wings) faces straight ahead.
Another resource is a slideshow with photographs of Yang Chengfu demonstrating each of the postures of the long form. Below: Yang Chengfu demonstrating lou xi au bu (brush knee push).
Yang Chengfu Taijiquan 108 Movements
Yang Zhen Duo, the youngest son of Yang Cheng Fu, would have been about ten when Yang Cheng Fu died, so I conclude that he would have learned primarily from his brothers. He offers a lengthy tutorial on the long form, much of which is lecture, at least in the beginning. I can’t say I got much out of the English subtitles and voiceover in the first hour. Demonstration begins at about the one-hour mark.
- Section1: https://www.youtube.com/watch?v=KANUIzDJS-0
- Section 2: https://www.youtube.com/watch?v=a6UIUJ3Aw9M
- Section 3: https://www.youtube.com/watch?v=P_acXEF3dQc
I found a set of four shorter videos of Yang Zhen Duo doing the long form (demonstration, no lecture). The parts do not correspond to the usual division of the form into sections; they are just equal-length (about 8 minutes) segments:
- Part 1: https://www.youtube.com/watch?v=t_hCCTTG3UY
- Part 2: https://www.youtube.com/watch?v=7MIUxiBC5uc
- Part 3: https://www.youtube.com/watch?v=FSAaqb30hfU
- Part 4: https://www.youtube.com/watch?v=xmOQUEQKbzs
The Yang Family’s website offers a list of movements, which differs on a number of points from the list above (transcribed from Yang Zhen Ming), but again, the difference lies mainly in the names, less in the execution of the form.
Tai Chi Notebook 
I am pretty sure that Yang Zhen Ming (1910 – 1985) also studied with Dong Ying Jie (1898 – 1961) when Dong and Yang Cheng Fu were traveling in the the south of China. Yang Cheng Fu was ill and returned to the north (where he died shortly thereafter) and left Dong to carry on. Dong then moved to Hong Kong which was his primary location until his death. Dong was one of Yang Cheng Fu’s senior disciples. Since he was 12 years older than Yang Zhen Ming, it is logical that he helped to teach the younger Yang his taijiquan. That would explain why Yang Zhen Ming’s style looks very similar to that of Dong Ying Jie.
Yang Shouzhong’s birth name 谱名 was Yang Zhenming. The brothers in that generation all share the character 振, as giving siblings a shared character was and is a popular naming convention in Chinese families. Chinese people used to have multiple names, but this tradition is fading away. Shouzhong would have been the public name, also known as a courtesy name or “style” 字, chosen or conferred in adulthood, according to which non-family members would address him. Literati would also have an art name 号, almost like a nom de plume. For example, Sun Yat-sen’s birth name was Sun Deming, with a pet name of Daixiang, but mostly he referred to himself as Sun Wen, a nickname he got from a teacher, whereas he was given the art name of Yat-sen in college, and is most popularly known as Zhongshan in China, after the name he got while in Japan.
Thank you for this information!