I am pretty much a nanny for my niece and do pretty much everything for her (laundry, loaning her money, getting niece up and dressed for school when she stays over 3 nights a week) and the list goes on...) while i work full time 3rd shift at a job I fucking hate. my sister is in nursing school.

First, stop being a nanny.

Therapy isn't an option as my family are super black and def play into stereotypes, they would not touch any kind of help even if they were paid a million dollars. especially my sister.

To her, showing any emotion is 'whining'. she yells at my niece all the time about it, she yells at me when I express emotion, etc. I go in my room and cry for hours and contemplate suicide. I think about killing her, killing me,

Look, you can't force others into therapy even if they'd profit from it. Seriously, I think it would be for the best if you got some distance between you and your family by moving out.

our grandmother recently passed and had...a lot of mental issues. never knew what she suffered from but was a very narcissistic, emotional, histrionic woman. and guess who was her favorite?)

It is very hard to deal with family members who have depression or other mental illnesses... sometimes it's just very overwhelming. To me it looks a bit like there's a lot of resentment from your sister's side towards you. I don't want to make up any excuses for her but to me it looks like her behaviour is some sort of a cry of help.

To her, showing any emotion is 'whining'. she yells at my niece all the time about it, she yells at me when I express emotion, etc.

How was your situation when you were growing up? How much attention did you need in comparison to your siblings? How did your parents treat your sister during childhood? Did they tell her she should "stop whining" since they've already had to deal with her sister?