Social stories will help. Has anyone called him a cry baby. Seems like he is bullying her because he has been bullied. He doesn’t have a problem with older brother because he was the baby till his sister came along. Probably jealous. I keep telling E, I am kind to you so you need to be kind to me. Teach him to be kind by being kind to him. Consequences/punishment will only lead to resentment.

I would read him a social story about hurting others, emotionally/physically and its repercussions. Also a story about siblings too, explaining his role of an older brother to his sister.
Here's a link to a website on these topics, there are various titles to choose from, just scroll down to check them out.
https://www.teacherspayteachers.com/Browse/Sear...

yeah, glad to see the recognition of repeating what he hears/sees. We're so used to this now with our son that if he says something out of the blue that is either mean or odd my first question to him is "Where did you hear that?" which is almost always followed by him telling us of a movie he's recently watched.

We've only got two boys, but our oldest (ASD) is VERY mean to his little brother (non-ASD). He has very low language ability, so doesn't call names, but pushes him all the time... which scares the heck out of me, because we live in a house with two long flights of stairs!! It's so hard to get him to understand that that's not okay. So far, we've dealt with it mostly by keeping them apart, or with another adult in the area. It's pretty distressing. I hope you find a way to make things better!!

Thank you all, I have gotten a few social stories to try with him and see if that helps at all. We are still “new” to this diagnosis and I didn’t even think of using social stories, we have visual signs on the wall that I made telling him what isn’t allowed but that’s obviously not working too well anymore. As far as I know he isn’t getting bullied or being called names in school, his teachers are amazing and would definitely let me know of something was going on at school. Part of the problem is he repeats what he hears, so after watching Zootopia he will go around calling people “dumb bunny” or saying he’s going “wreck” someone/thing after watching Wreck It Ralph. He repeats movie/tv show lines or things he hears from other people which is not helpful at all.