From the Ramban in Beraishis 26:5 it seems that not only Avraham Avinu kept the Torah, but also his descendants, including Yaakov, Yosef, Amram, Moshe etc. He derives this from the passuk "that he [Avraham] commanded his children and his household after him to walk in His ways".
According to this opinion of the Ramban, How far did this continue? Did all the descendants of all the Sh'vatim (All the (future) Jewish people up until Matan Torah) observe the Torah before it was given?
