Not a big believer in being "lawsuit happy" - especially in a case like this.
1. The boy is a 17-year-old kid. He's just a boy whose younger sister told him that some old guy raped her. Was he thinking clearly? No, but 17-year-olds often don't think clearly. Hell, I can easily think of a 29-year-old who represents the Bronx who can't think her way out of wet paper bag. BUT, he committed second-degree murder and he needs to be prosecuted, judged, and sentenced, accordingly. If you sue him in civil court, I am sure you would win, but he won't have any assets to turn over to the plaintiff - blood out of a turnip.
2. Seems to me that this 16-year-old girl has some real issues. She needs help, desperately! HOWEVER, she also needs to be prosecuted, judged, and sentenced for filing a false police report and for inciting her brother to murder.
3. I do not believe it would be right to go after their parents unless one or both of them helped to incite their son to commit an act of murder. I cannot imagine what it must be like to be the father of those two kids, right now. How would you like to innocently come home from work and find out your daughter made fake claims of rape and incited your son to kill an innocent man? Whoa!
This is a tragic tale. One that is a predictable result from all the insanity fomented by libtards in their promotion of histrionic victimology.