Is this call domestic violence

My parents got green card, and live with us. They fight very often, my dad can find any excuse to fight with my mom. Sometimes he say somethings that's beyond anything you can imagine....... Sometimes he went to kitchen and take the knife, threaten. He also pushed my mom to sofa, cover her head wit blanket. And he is trying to control our life, make everyone in the family live with high pressure. He wanted to interfere with our daily life, try to make everything difficult for us to do. We have do daughters ( younger than 10), I really don't want the kids to hear this. But I also don't want to send my parents back to China, since I am reall afriad he will harm my mom. What should I do? I told my mom, if he ever do this again, she should ru of of the house and scream for help. I think people will call 911. Yeh, I maybe able to call 911 myself, but they are my parents, it's hard to imagine that I did this. So if someone called 911, will police take him away and send him back to China? That will be ideal for us. What will the police do to my daughters? Will they be sent to foster home? Since this is really not our problem, it's my dad's problem, but he lives with us. Thanks for any advice