From what I delt with being adopted my my mom treating her blood relative better than myself because I'm not her real family. But that's different. Here's what I see.
Honestly. It depends on your age, if you're in your teens, not 17 or 18. You can probably get help from emotional abuse. If you're an adult living with your sister and mom, move out, find someone who has the same problems and make a bond. If your sister tries to call you, stop by your house, you can probably tell someone that she's harrassing you and to get her to stay away from you.
Narcissists only occasionally recognize their own narcissism! Even if they do, they rarely care.
no
Short answer? You don't! You let them find out about your sister on their own (and they will, eventually). Continue your regular (hopefully good) relationship with your in-laws as you do now.
Seeing as your sister is not a boss in a video game, I'd say that you don't and that your sister probably isn't old enough to be an actual narcissist.
Your mother's sister is your aunt.
Your mother's sister is your aunt.
Your mother's sister is your aunt. Your mother's mother is your grandmother.
Your mother's sister is your aunt.
Mother Teresa's sister would take care of her mother then her mother died and after the death of her mother, Mother Teresa's sister had died!
Your dad's sister in law that is your mother's real sister.
Your Mother's Sister Is Your Aunt.
Your mother's sister is your Aunt. You are her niece or nephew.