Not to get too much into it, but my mother is one of five children. One of the sisters estranged herself from everyone. Then my mother went No Contact with them, too (cutting my sister and I off from everyone). Since FaceBook, my sister and I have a little contact with my moms family, but we arent very close.
Theyre not awful people, IMO. Theyre regular people with personality flaws. My grandmother was supposedly a toxic narcissist, and so was the aunt who went No Contact decades ago.
Heres the twist: My mother, frankly, is toxic, herself. She does the things she claimed THEY did. Sometimes the person leaving the family behind is the one with the problem.
AND its an abusive technique. If you can manage to alienate your intimate partner from their family and friends, theyre more dependent and easier to control. ABUSE 101.
Just to follow up on this (I agree with a lot of what you said), I come from a multi-generational family where my brother and I, Mom, grandparents, and great-grandparents all check the boxes for adult Cluster B personality disorders. I'm the only one whose been diagnosed, though my brother and I both see it in ourselves.
The thing is, it plays out differently in different relationships.
My grandparents were amazing to me and my brother. It didn't even feel like they were hiding a dark side or putting on an act. They just connected to us in a very warm, mostly healthy way. But we only saw them a few times a year.
It was a completely different story with my Mom. My grandpa was emotionally abusive to her for her entire life, until he passed away, and my grandma enabled it. He encouraged abuse from her older siblings, too, and played all of them off each other. My brother and I only got a glimpse of it when my grandfather's guard went down, or he thought we weren't in the room. My great-grandfather, from what I've heard, was the same way. He ended up committed suicide by leaving the car running in the attached garage of their house. If my great-grandma hadn't gotten up in the middle of the night to get water and found him, he probably would have taken her and their still-teenage children out with him. Guess how my Mom remembers my great-grandfather? As a super warm, kind man.
In turn, my Mom was incredibly unstable with us, going from codependently attached to violent on a dime, and still is. But with everyone else- i.e. those who she keeps at arm's length- she's a constant ray of sunshine. As adults, my brother and I constantly play a balancing act between keeping our sanity and our emotional distance from her, and pushing back against people who know her at a superficial level, find her delightful, have sympathetically listened to her sob stories about how mean we are to her, then reach out to us specifically to accuse us of "making her miserable."
So, I totally get what you're saying. At least for some people who are visibly toxic, though, the behaviors can seem to come out of nowhere or be limited to one child, when really there are behind-the-scenes dynamics that are very well-hidden for a reason. It's been kind of bizarre, for instance, for both my brother and I, to be consistently pegged as the source of all my Mom's problems when we've been taking ownership of our own toxic behaviors, and encouraging her to seek out therapy to improve the quality of her life, for going on ten years. It's really hard to see the whole picture sometimes, even when you think you know someone well.