AITA for "choosing" my step son over my biological daughter Update

I have 4 kids all together. My daughter and step son are both 26. My other daughter is 23 and my baby boy is 14. I don't like my oldest daughter's husband and how he speaks to my grandson. He yells at him, calls him stupid. Yells at him to stop crying before he pops him in the mouth. My daughter defends this by saying it's how he was raised. He's just trying to raise their son to grow up into a strong man. He's 4! He is so hateful to my grandson. I don't know how my daughter is just okay with this. It's clearly not working because they've had meetings with his Pre-K teacher and she was trying to tell them that he has severe anxiety. So they just decided she's dumb and pulled him out of school and plan to homeschool now. Which is crappy because he did like school. He just has really bad anxiety.

Anyways what happened is they came over for a Halloween party and my step son was there with his partner and step kids. Him and his partner aren't married but they've been together for 6 years and he adores the kids. At the party my step son's step son was trying to use the bathroom and was taking too long so my daughter's husband was yelling through the door and when he came out was yelling saying other people have to use the bathroom, are you stupid, the stuff he says to their son. My step son and his partner got upset and said they were leaving. When I found out what happened I said they don't have to go and they said they don't feel comfortable around him. I said then he can go. My daughter was upset about that and I said her husband is disturbing people. He has no right to yell at other people's kids like this. My daughter said "Well he's my husband and my family. If he goes, then I'm going to!" I told her that I'm sorry. If that's what she wants, then she can go too. She was mad and they all left together. Since my daughter has blocked all of us on social media. The last thing she said to me was over a phone call and said until I apologize shes cutting us off. I don't want to b cut off by my daughter but I also don't think it's fair that I apologize. Her husband was being his normal hateful self towards. I don't even know why he had kids because he doesn't seem to like them very much. But AiTa for making my daughter leave instead of letting my step son leave.

@Jaja I didn't cut her off. She's threatening to cut me off. I'm not saying there is no possibility he's shitty to her but he mainly has this attitude towards children. Her husband respects adults but doesn't think children deserve respect. The reason why I think my daughter has just as much a part in this is because she also has this idea of how a man should be. She's always said her son's will be raised harsher than her daughter's . I just didn't expect this harsh. He could be crappy to her too but honestly this is just how this guy treats children. He's said himself he believes respect is for adults, not kids. He just doesn't respect children.

Update: Me and my daughter tried to talk it out over the phone. She admitted that maybe he shouldn't have shouted at her step brothers kids but that how they choose to raise their son is their business. I told her I understand that and this was all over him yelling at my step son's kids but she really should think about how they treat my grandson. He's 4 with really bad anxiety and she tried to say he doesn't have anxiety. The teacher is an idiot and this is why the generation is getting weaker. I tried to reason with her and tell her that I understand her and her husband want to raise a strong man but he's 4. Yelling at him all the time and not allowing him to cry is just gonna cause problems in the future. She said as long as her son isn't weak or "rrtarded" she's fine with whatever. The conversation got nowhere but I think we are at least on talking terms. I know people think I should call CPS but my daughter would never forgive me.