Suspected Child Abuse/ TW.

Hello ladies, I am having a hard time trying to decide what to do. My childrens father and I split up in 2018, he got remarried in 2019 to somebody who, honestly, is a terrible person, she has a 6 year old son, and I've heard her threaten to kill him, hit him, and just overall is a horrible parent to him (I've reported the abuse 2 times and nothing has been done) .. Unfortunately, my ex husband and I have 50/50 custody, we have 2 children together, a 5 year old non verbal autistic girl, and a 2 year old boy. Neither of my children can clearly communicate what happens at their fathers house, which is scary to me. The last 2 times I've went to meet with their step mom to pick up the kids my daughter had a nervous breakdown, full on screaming and shaking just pulling into the parking lot we meet at. Im terrified that his new wife may be hurting my kids, and my children can't communicate that with me. I do not know what to do. I just want all of the kids safe, including the one that isn't mine.