Hi,
I'm sorry your relationship with your sister is not good - my closest relationship in my life is with my sister and I am eternally grateful for that.
I do have an Aunt that I choose not to be around - she is very religious and forces it on everyone around her, so I chose not to be involved with her.
My mom would ask me to go with her to see her and to do it for my mom. I finally said to her "why would you want me to be there when I am going to be miserable and your going to be nervous the whole time that I'm going to tell her to stick it?".
She finally got it and no longer asks me to go
You do have the right to do what makes you happy!!
Tranquility