So sad!
Our family was - still is - characterised by a bully father. Siblings have resorted, in adult life, to being the bully or the bullied. Clear demarcation. I was the bullied but the worm turned and I did an about-turn, got into therapy and explored the family dynamic that had set me up for it. My family, for various reasons, are not prepared to explore this dynamic, prefer to stay in their roles as bully/bullied. In fact fight for that dynamic to stay on its wheels. I am not popular, shall we say.
If my [shocking bully ] elder sister acknowledged she has been bullying towards me that would go a long way with me. If she took responsibility for it, instead of blindly insisting on perpetuating the family poison, that would be something. I can only conclude - and I don't want to sound snooty here - she hasn't suffered enough to need to plumb the depths to change what is intolerably painful for her. As it is, it suits her well and she is not in a hurry to change it.
I do bridle a bit at the term 'teasing', especially if it has 'cruel' attached to it. Or the chilling, and wholly accepted, notion of 'sibling rivalry'- as though it is not serious, just one of those things, let's not be sensitive. It minimises what was, simply, abuse. Extremely damaging abuse in my case, with disastrous, lifelong, consequences.
You may not want to accept you are A bully, tormentil, but can you accept you were bullying? It was the family system, as it is in my family; but taking responsibility for our behaviour, however schooled we were in it, goes a long way to unlocking a dynamic that destroys, whatever end were on it.
My sister has her issues, certainly, and I do have compassion for her on that. BUT not at my expense. I am not saying that the way things went was your fault, tormentil, but you are suffering as a consequence of what was a toxic family system. They probably are, too (your sisters). I have been a shocking bully in the past - like you, it was all I knew - and I have had to accept what i did and apologise, if appropriate. I know i was innocently bullying, if you like, but i did it nonetheless.