The plan concocted by the sons of Israel was to kill Joseph and then lie to their father.  On the surface, it seems all of the brothers were in on the plan.  However, if we listen to the rest of the story, we find they were not all on the same page. 

Joseph is sold to a caravan of traders, Ishmaelites and Midianites, on their way to Egypt.  The Ishmaelite's were descendants of Abraham and Hagar’s son, Ishmael.  The Midianites were descendants of Abraham and Keturah’s son, Midian.