There’s Illegal and ILLEGAL. If they were robbing banks or shooting people down on cold blood with real bullets- maybe.
But what they are doing is violating Constitutional rights, etc, Federal laws, which generally require Court orders and decisions. So, yes, the ACLU will likely win several of their cases, which will prove (some of what) what they are doing is illegal. But not ILLEGAL.
So yeah, Federal courts may rule they have to stop- in fact one court ordered them to stop harassing journalists- and they didnt stop. This may result in court orders, contempt, etc.
But if they have violated state laws, they likely have done so under color of authority, and the state likely cant touch them- without a court order that is.