I have two nieces, and 8 year old and a 4 year old (sisters). The 8 yo has been a difficult child since she was a toddler, and the 4 yo is just your normal, cute little kid. The 8 yo has been spoiled relentlessly, and at 8 is still having vicious temper tantrums, screaming until she pukes, throwing things, breaking things, slamming doors, etc.
On Friday night, her little sister accidentally spilled a little water on the 8 yo’s sock, and she went ballistic - yelling at her, kicking and punching her, telling her to get off her couch. While getting off the couch, the 4 yo spilled a little more water on her sock. The 8 yo went even more nuts, then - she took off her sock and threw it at her sister, yelling that it was hers now because it was ruined, hit and kicked at her sister some more, and yelled at her “I hate you! I’m going to kill you!”
I realize at 8 that she doesn’t completely grasp the seriousness of what she said, but the whole situation seems really bad to me. I don’t have kids, so I don’t know if all kids go through a “death threat” phase.
How serious is this? Is there any advice I should be giving my sister and brother-in-law regarding this situation? (My sister is too weak to discipline properly, and my bil doesn’t think there’s any problem.) I know I don’t have very much (if any) say in what goes on in their house, but I don’t want to do nothing and regret it later if my niece seriously messes up her life, or, God forbid, hurts her little sister.