In Yosef's case, we see a teenager, forced to work as a slave, who can perhaps improve his lot if he gives in to the seductions of his master's wife. Yehuda's descendant Nachshon ben Aminadav inherited this strength and demonstrated it by being the first to jump into the Red Sea, even before it had split. Going a whole year without working the ground requires a similar show of supernatural strength and faith, says R' Chaim Yishayahu Hadari, shlita. Indeed, developing this strength is one of the purposes of shemittah. Many explanations have been given for the dispute between Yosef and his brothers.
Most commentaries attribute the brothers' enmity to philosophical disputes.
Chazal say that the Patriarchs observed the Torah. Thus, Ramban and other commentators strain to explain how Yaakov could marry two sisters, something which the Torah prohibits. Chazal say that Yosef accused his brothers of eating meat from a live animal. Yaakov's sons of course slaughtered their animals in accordance with halachah, since they all agreed that they were required to keep the Torah's stringencies. Yosef disagreed, however, and felt that before the Torah was given, the Torah's leniencies could not be relied on.