Mom left bc of husband

So my mom just left our house because of my husband. She came down for Christmas and was going to take our oldest (8) back to PA w her tomorrow for her dad but they just left. All because of the way my husband speaks to our oldest (my child not his bio). I don’t even know what to do. I agree that he is nasty when it comes to her.. he’s just mean. Yeah she doesn’t listen sometimes but he doesn’t have to be nasty. Well our 8 year old and 5 year old weren’t sharing nicely and he started yelling. My mom told him to stop yelling and he started yelling more at her. So she said this is enough, we’re leaving. And they left. 😭 I don’t even know what to do or think anymore. He’s taking it as disrespect in his house, but my mom is taking it as protecting my child. She’s always had an issue with the way he speaks to her. He’s just very “in the adult and you have to listen to me” lay down the law type of person. I don’t even know what to do I feel like I’m supposed to pick sides.