<human>: For quite some time now I (19F) have noticed that my sister's (14F) rude and abusive behaviour has escalated. She is constantly verbally and physically abusive to members of my family. Just yesterday, she threatened to kill herself if my mother cut her cellphone plan. My parents constantly spoil her and have given up dealing with her behaviour so instead of disciplining her, just give into her every whim. She physically attacked me yesterday leaving several bruises and pulled out the kitchen steak knife to threaten me. 

As for those who think my sister deserves a smack in the head, I agree however, she on several occasions has threatened to call Child Protective Services if my parents attempt to spank her. I don't know how that process is conducted but with two other under age sisters in the house (9F, 15F) my parents rather not deal with that situation. They never follow through with their actions, saying that they will ground her for the weekend, or forbid her from watching t.v or cut her cellphone service- however that never happens. 

Please reddit, as the oldest sibling I feel the need to reach out to her in some way and protect my other sisters from her torment. She will not listen to my advice and is headed down the wrong path. What do I do?

Can you give me a shortened version of the text?
<bot>: My (19F) younger sister (14F) is constantly verbally and physically abusive to several members of my family. My parents have given up on disciplining her and as such her behaviour escalates. What do I do?