I have 2 sisters, Janet 21, Sally 14. I am the oldest.

Growing up, Janet was a liar, manipulative, anger issues, promiscuous, disrespectful to father. Mother always took her side undermining my father all the time (refusing to let her out past 10, etc...) This lead to them no longer "loving" each other and plan to get divorced now (They currently all still live in the same house). Janet married some army betabucks and moved out for like 2-3 years. No surprise they are getting divorced now, Janet and her Husband (I don't blame him).

Janet has moved back and has not changed. First couple of days she seemed nice but I could smell the BS. I don't live at home, and my concern is how she treats my other sister Sally (14). Janet is nice to her but over any minor disagreement she says nasty disrespectful things to her and that really pisses me off to hear she treats her like that. She is 14, and I don't want her to grow up with shitty self esteem or become a nasty person like Janet.

What can I do? Should I just let them be and concern on myself first? I don't live with them I have my own place. But knowing in the back of mind my baby sister is being treated like shit at times makes my blood boil. Once my parents divorce is complete their plan is to move in all together (mother, janet (21), sally (14)). Please.