Disagreed on Fredo; his problem was jealously of his younger, smarter brother. So jealous that he betrayed his brother and, therefore, his entire family.
Agreed that Fredo had other options such as coasting or working hard on his own without setting himself against his own family.
Michael put the hard work into school, college, and then finally heroically serving with honor in WWII. These are all laudable actions to us, but to his family, he was not putting in the hard work. Sonny(the oldest son) began committing crimes when he was a teenager, and continued committing crimes when a normal person (like Michael) would have been going to college and serving in WWII. In that family/organization Sonny's crimes was seen as the hard work. So Sonny was the natural choice as leader/godfather when his father died. Michael was willing to put in the hard work when there was absolutely no one else willing to do it, for instance killing the police officer, but he really wanted someone else to do it.
When Sonny died, Michael had to take over the leadership. Michael was no ones first choice (not even his own). Fredo was stepped over, because he would not put in the hard work. If Fredo had been willing to put in the hard work, he would have been the second choice after Sonny. Even if Sonny had lived, Fredo would have had a high position in the organization. Or Fredo could have accepted that he would not have a high position, not put in the hard work, and just coasted. He would have been taken care of, and had a good life.
Fredo wanted the high position, but did not want to put in the hard work. That left him the option of finding another organization willing to give him a high position without hard work. The reason another organization was willing to do this was that Fredo was betraying his own organization/family. In that way, we are both correct.
Obviously, all this is just what I see in the movies. These people are not real, and the movies are not real.