OK, my DL armchair psychologists, can we talk about my family?

I have this motley group of cousins, and of course I am the family outcast for at least 3 decades now, but we all got together after several years to celebrate our generation (ALL OF OUR Parents are dead) and I had one aunt in particular who was a psychotic monster. She had 3 kids. Two boys and a girl, baby in the family. Mama doted on her daughter, but was both mentally and physically abusive to her sons. One son is dead (Cancer) the other has severe mental health issues, lives alone needs a service dog and avoids certain people and situations as "triggering." Daughter is married, with kids, and has a successful law practice and marriage. But daughter has issues too. She's a passive aggressive type who pumps people for information than shit stirs and uses it against them. She pretends to be neutral and wants everyone to get along and practice kindness but she is among the top most destructive gossipers in the family. I was able to observe a lot at our gathering. Being an outsider is helpful that way. My question to you all, is t his. She was not a direct victim of childhood trauma, but she obviously experienced it second hand. She and her one living brother are only 11 months apart, but the dynamics are odd. They get together for a meal three or four times a month and she humors him but she also manages to keep her distance from him. She has always come across as wary and observant and can be snippy and uncommunicative. So I am wondering how an abusive mother affects the one kid who was not abused? I'm just trying to figure t his out so I can avoid certain traps.