Firstly I would say I want honest advise/opinions even of they are horrible or you think I'm being a bitch 
My sis is two years older than me and is nuts quite frankly. She is an alcoholic, she lies all the time and she has quite bad mental health problems which she won't get proper help for.
To give a few examples:
She accusedy partner of robbing her house when he has never even been there.
She has accused my parents of doing unspeakable things to her that are not true
She claims she would've a better parent and wants to take me to court for access to my kids (she has never even met ds)
She wrote my dd who was 4 at time an Xmas card saying me and her dad were arseholes and that's why she hadn't seen her ( it's now been three years since last saw her) an clearly expected us to read this to her.
There are many more examples if people want them.
My parents are upset as they are stuck in the middle which I do understand and it's worse now with build up to Xmas. I know she is my sister but I don't trust her at all. Even when she is supervised by us she manages to cause an argument or bad atmosphere etc.
Any advice?