As far as your Xh's aunt goes, I'm sure you wondered how her H managed to win over a woman like her, too. A Prozac marriage--I guess that's settling!
That's absolutely true, about being careful what you wish for. You know that old saying about how you should see how a man treats his mother to know how he'll treat his wife ... though, judging by your MIL, that's probably not an adage you were too concerned about ... well, I was attracted by how loyal, admiring, etc, H was of his M. Until I saw her slimy underbelly and realized he was choosing her over me.... Why is it that whenever you think you've done well in the lottery of life, you always then proceed to get the (unexpected) fine print on the other side of the lottery ticket smushed in your face?
Wow, it's scary to think how close your step-son came to being molested himself. Your XH did well there to prevent that. I feel for his brother, though. I've found, and heard the same thing from other abuse survivors, that we have dreams of molesting our children. We wake up horrified and disgusted, wondering WHY we had such a dream. I can only speculate that it's to enhance our awareness that we're not choosing to go that route, and haven't got that desire. One friend had thoughts like that during her postpartum depression and worried she was really going to molest her newborn. It's good your BIL was able to distinguish between dreams and thoughts, and actual urges, and that he was so determined to do the right thing.
At the same time, it sounds like there's still a lot of denial in the family, though I can understand why it would be hard to discuss it more openly, which is impacting on the siblings' lives. I can't fathom perpetrating so much evil in your children's lives, PARTICULARLY if the same thing was done to you as a child. It must have been difficult for the sister not to have her own abuse verified and acknowleged.
But ... at least all of that is not your problem anymore! If you didn't care for imaginitive writing, I know our local colleges and universities offer courses/workshops on journal-writing and writing what you know. I thought, you're obviously quite intelligent, so it might be a way to meet new people with whom you feel compatable. Plus, organizing your thoughts on paper can give clarity and make a "pattern" from all the jumbled thoughts in your head. For some people, once they've put everything "out there," they find they don't need to dwell on it much further.