What can I do when sibling taking advantage of older parents?

For the past 2 years, my nephew has been living with my parents (who are both retired). As my sibling and their partner cannot handle the "outburst" and "attitude" with thier son, sometime they have been violent. Their son decided to move out and "refuses" to go back to their home.

His abusive behaviour is also being done to my parents.

Both my parents have recently had surgeries, and I feel this situation may affect their health and recovery. They do not requrie additonal stress in any means.

When I confronted my sibling that the situation, that has been happening over the past 2 years, needs to be addressed and our parents should not have to deal with the abuse, raising a hard to handle teeen, and also cover all monetary costs (as my sibling does not provided any financially coverage to my parents either).

My sibling feels that I am attacking their parenting skills, and that since I live 200 miles away, I have no say in what is going on, and don't understand the circumstances. And atop of this tells me directly. that since I don't have any children of my own I wouldn't understand, and shouldn't tell them how to parent their children.

However, from what I am being told directly from my mother, who is too scared to confronty sibling, as she feels the only option would be for my nephew to live on the "streets" or "couch surfing".

Now these past few months things have progressed negatively even more, recently found out that my nephew has been involved in some illegal activity.

I'm at my wits end, trying to get my nephew out of my parents house, but don't want him ending up on the street either.

I live 200 miles away, and am at a loss as to what to do.