It's heartbreaking.
They scream at their children and their children are starting to show the same signs of a volatile household that my sisters and I did as children.
My husband and I have made it a distinct, deliberate point to raise our baby in a calm, loving household where we don't use yelling as a way to resolve anything. Unfortunately, my sisters-- who think they have life figured out and will continue to remind me of it-- scream at their children, physically drag them around, make them feel awful about themselves, etc. They think they're excellent parents.
Here's an example: My uPD older sister's youngest child (6yo), who may have an undiagnosed mental/behavioral disorder, defecated outside near the back door. I thought it was dog poo, but he exclaimed that he did it-- without regret. My mother and I were afraid to tell my sister, but she came outside and saw it. She grabbed a plastic bag and picked it up, then came outside and practically rushed her little child, yelling at him. "I can't believe I just had to pick up your POOP! That's DISGUSTING. You do NOT do that!" Just absolutely screaming at him, just like my uNPD or uBPD father used to do to us. She was humiliating him and he was crying and calling her names. She took his toys away. Later, she walked away and he said, in a sad voice "She tells me and {brother} to just let things go after a fight, but she never lets it go! She never forgets it!" And he cried more. Then I asked if he wanted to come with me to go for a ride, and she overheard and said "I will NOT reward him for this behavior." Her face was red and she was holding it against him. She never asked him why he would do that, she never talked calmly to him, she never hugged him. Ever. She was embarrassed and took it out on him.
I had to walk away during the event because my own child was scared of her. I'm afraid of her anger, too.
And then my diagnosed BPD younger sister, recently: Her also 6yo son didn't want to go home from his grandmother's house yesterday and he got sad. She escalated it and screamed that he won't be able to EVER stay home from summer camp again (because he was allowed to that day) and "actually, [you] will not be spending time over at your grandmother's AT ALL." The same type of threats my uPDfather used to give us. Then she walked quickly at him and he said he didn't want to clean up before leaving and she yelled "WHAT DID YOU SAY TO ME?!" and he screamed and ran. Then she came back to my mom and I and said "WHAT?!?!" defensively when she thought my mom and I "looked at each other." I didn't look at my mom, but I know she was paranoid that we were uncomfortable with how she dealt with the situation.
I'm so disappointed with them. They are perpetuating the problem. They are continuing the cycle. My older sister enables my father and infantilizes me and my mother. My younger sister demonizes my father (rightly so), but acts just like him. My older sister's oldest boy who is 10 years old said he has a "troubled childhood" to my husband. My husband and I are just going to make sure that they always have us to talk to and to understand that it's not normal to be afraid of your parents. That's the only reason we're not going full No Contact with them...we want their kids to have someone to talk to.