You are a good brother!
I am thankful that your sister has both the family and friends supporting her, and that she has taken the steps toward personal protection and safety.
I have a niece (wife's sister's kid) who could not come to visit for Christmas, because she is being stalked by someone. She needed to be back in Kansas for a Court Hearing to get her "ultimate" protection - A restraining order. This side of the family thinks fighting back and guns in particular are EVIL. I have tried to get her, her husband, and her parents to sit through an informal
Refuse To Be A Victim class that I will tailor just for them, but "that is wrong." The police will protect us, and the Court is "granting" her a restraining order. "All will be good, and nobody will get hurt."
GRRRRRRRRRRRRRRR!!!Now the other side of the family, my sister's daughter has four spawn, and here is a family photo they had taken last week:

Not saying we are a family of action, but it was these boys uncle who made me an offer:
When our now ex son-in-law went bad, our loving nephew, uncle to these three boys, offered to make him disappear. He promised he had friends that would help him, and nobody would ever know. Nice to know who has your back, but we thankfully declined as we brought her into a safe setting.