Why am I such punk when comes to my sister's? Advice please don't be mean.

I am always one to be there for them. I am second oldest on my mom's side. I am third on my dad's side. My mom addicted drugs has been since before I was born. I had help take care my sister n brother n then my oldest brothers kids when he got addicted drugs. I met my dad at 16. I was same way off bat with my sisters from dad. Even after my older sister kept stabbing in the back last time when our sister died .I had custody of my niece she lied said I was reason she didn't have a relationship with her mom. I didn't defend myself to my niece the truth is out sister was on drugs n an alcoholic. But how tell a child that lost her mom that. I simply held my head down and walked away. The thing is this same sister I always help kids need something I'm there. Nephew had have surgery I'm first on scene. SHE needs money there. In this way all time with all of them but always treated badly. My deceased sisters birthday is coming up I want go grave sight but I don't want run into them. My other sister let's call her Kathy is really mean she calls me fake says I'm not her real sister. SHE even went as far to tell my dad that a therapist said it's ok for me not be in my nieces life. The thing is she won the case because I refused to do her way she did me. I know a lot bout her but I was taught by my granny take higher road so I feel like a coward. What's wrong with me???