CPS help

So my sister recently lost some custody of her child to my mother and my father only because her baby daddy beat her son and because she didn't have a stable household (she left her baby daddy and has been in a stable relationship but they used the past against her)

they got some custody.

So my mother changes in front of him, take showers with him, Wipes his butt, Washes his body in cluding his p p, sleeps with him In her bed, he is 6 years old he can do all of these by himself. (He also is using the bathroom on himself and he was hording his dirty underwear in his room and not telling anyone, he is doing bad in school also again etc.) My sister before she Lost some custody had decided to make it where my parents only got him one time a month so she could make him stop using the bathroom on himself, do better in school and stop talking back and doing all the bad things that he was doing, And it was working he literally stopped everything, but as soon as he went back it restarted and I got worse and I told my sister it sounds like she might be doing stuff to him. My dad doesn't act like this.

She does not care about my children she only cares about my sister's child so CPS told her there is nothing that they can do.

So is she just supposed to just let my mother groom her son?

Keep in mind she never did any of this with me or my sister we have an older brother, but because I was not alive i don't know how she treated him. But when I was younger he raped me so I told my sister.

Beforehand that my brother did not turn out the way he did from no reason likely my mother did it to him too.

So what is she supposed to do?

They are the type of people that follow everything to T they know that you're watching them so they're not gonna do nothing visual.

But they also do stuff out of spite, Like my sister is a great mom I don't know how this happened

basically my mother asked if she could have time with her son at school during lunch time, And instead of eating lunch with him she took him to social services and got him to say that stuff about his mom. Because she tried to make him do better.

She baby's him to the T so much it's creepy, so if he was told that he would get something he would have liked to get it. He is a child so that's how they are. They don't know the difference between right and wrong.

Like I said she does not care about my kids it's just him which is really predatory behavior I just don't want her son to turn out like my brother what is she supposed to do?