19. In Gen. 50:20 does it mean that God meant Joseph's brothers to sin against him? Can God ordain that people sin?
This requires a complex answer. God does not cause sin. He does create people who sin, so He can be said to be a secondary cause of sin, but we cannot accuse God of breaking His own character, which is holy, complete, perfect, etc. He is incapable of sinning.
Several times in Scripture, however, the hints are floating around that God USES sin, catastrophe, etc. for His own good purposes (Romans 8:28 most famously), and does NOT prevent all catastrophes from occurring.
Google "Alvin Plantinga" for a series of essays on good and evil. He's done some wonderful work on this topic.