Sister/HalfSister/StepSister

Vanessa
It's been one of those days. Super long story. 
 my whole life I've lived with my mom & dad, 3 halfsisters who are all older than me, when I was 8 my younger brother was born & my little sister was born when I was 16. When I was 4 my dad brought my halfsisters to live with us & I was super excited. 
I hated being an only child & was glad to have them around. My whole life I always thought of them as my sisters. Not step or half. Just my sisters. I looked up to them, was proud to call them my sisters. 
They pretty much rejected me from the start but never called me anything other than sister. We have gotten along better over the years (at least with the one closest in age to me) & spend at least one day a week with her. (They all spend the weekends together & I'm never invited, neither is my little sister) I've babysat my 6 nieces & nephews since they were born & am pretty much responsible for them having learned to read, write, do math & so many other things. 
So I've been around all of them almost on a daily basis even though we haven't lived together for years.
Recently my sisters were able to meet their mom & reconnect with her and her 6 other kids who are their half siblings. Ever since then, they refer to me as their stepsister & those 6 other siblings as brothers & sisters. Not step or half. They've even begun telling my nieces & nephews that I'm their stepaunt. This really bugs me because they tell their kids (who are half siblings) that they are brothers & sisters. Not step or half, I don't know what to do about it. 
It makes me want to just cut ties with them & walk away. Anyone been in this situation before? What do I do?