I got a chance to talk to Yang Jun yesterday about your question. Let me summarize his response:
The Yang family no longer practices xiao3 jia4 or small frame. Yang Banhou had few disciples. One, at least, was Quan You, the father of the well known Wu stylist, Wu Jianquan (Quan You was a manchu, and had an unusual surname, which in the next generation was changed to Wu). It is true that the Yang family used to practice some kind of kuai4 quan2 or fast set; it appears to have died out with Yang Chengfu's generation. Yang Shaohou learned a lot of his art from Yang Banhou. Not that much is known now about Yang Shaohou's forms, though it is unlikely that Ma Yuehliang learned directly from Yang Shaohou.