The worst thing is my parents' mental illnesses. My sibling and I flourished in spite of them. At least, we only had to deal with them one at a time: my mother had custody and we rarely saw my father. I had seen him after a 30-year hiatus and it was just as well. I haven't seen him in >10 years now and likely never will. My mother developed vascular dementia, which finally led to her personality disorder being diagnosed.

Fortunately, I have good extended family on both sides.