Yang Jun's reply in Chinese can be found here
Here is a translation:
From the point of view of objective history, there is no conclusive explanation of the origin of taijiquan. There are many theories, and those involving Jiang Fa are relatively common. Jiang Fa lived during the same period as Chen Wangting. Jiang Fa was a native of Hongtong county, in Shanxi province. He excelled in tongbeiquan (literally 'through the back boxing'). Tongbeiquan is still very popular in Hongtong, Shanxi area even today. Chen Wangting was a famous military leader at the end of the Ming dynasty and the beginning of the Qing dynasty. His barehand and weapon skills were very good, and he is known for having cleaned up the bandits in the areas of Henan and Shandong. There is a tradition that because Chen Wangting saved the life of Jiang Fa, Jian Fa owed him a debt of gratitude and so followed Chen Wangting. According to one story Jiang Fa taught tongbeiquan to Chen Wangting, so that his relationship to Chen Wangting was both friend and teacher. Another story is that Jiang Fa was a disciple of Chen Wangting. There is no definitive explanation or proof of their true relationship. I have discussed this matter with a famous teacher and representative of tongbeiquan, and according to him, in the the current Chen style second routine Pao Chui (cannon fist) there are many moves which very much resemble tongbeiquan. In the Chen family they have a painted portrait, the subjects of which are Chen Wangting and Jiang Fa. This confirms that a person named Jiang Fa existed and that he had some position with regard to the Chen family. That Yang Luchan studied with the 14th generation Chen family member Chen Changxing is well established and not disputed. Yang Luchan went to the Chen village 3 times and spent a total of 18 years learning their art, and was one of the most expert practitioners of Chen style at the time. The linkage between the Yang family and the Chen family runs very deep. My grandfather is entered into the Chen family records as a member of the 18th generation and has very good relations with the current Chen style representatives Chen Xiaowang and Chen Zhenglei. Whenever the two of them encounter my grandfather they refer to him as 'shi shu' (senior fellow disciple) and whenever I see them, I also call them them 'shi shu'.
Wu Yuxiang first studied with Yang Luchan. Later he went to the Chen village in hopes of becoming a disciple of Chen Changxing, but because Chen Changxing was already very old at that time and did not wish to take on any new disciples, he sent him to the town of Zhaobao to become a disciple of Chen's cousin Chen Qingping. Wu Yuxiang and Jiang Fa did not live in the same time period.
Wang Zongyue (lived during the Qianlong period of the Qing dynasty, approx 1736 to 1795) was a native of Shanxi. He lived in Henan in the vicinity of Kaifeng, Luoyang. His profession was teacher. He was a plain person who greatly loved martial arts. He was expert in taijiquan (it is said he learned taijiquan from the Zhang Sanfeng lineage of the Wudang school), spear, and sword. He authored a book called Taijiquan Pu (Manual of Taijiquan). Wang Zongyue and Chen Wangting did not live in the same time period.
In regard to origin and history of taijiquan, in China there are many historians and amateur scholars who have tried to sort this out, but up until the present, there are still no definitive conclusions. In recent times the most popular tradition is that taijiquan no doubt originated from the Chen family. The matters that I have related above are not definitively proven by historical fact or documents, but I have provided them for your reference.