Apologies if anyone finds this upsetting. Very hard to talk about this IRL.
In my perception it was abuse not experimentation but I am looking at this from my mother's POV.
I was 8/9, sibling 3 and half years older.
This was in the early 80's so not much in terms of support organisations. Definitely no one outside immediate family could know.
Older sibling was very much a golden child who could do no wrong. I was viewed as a demon.
I have no memory of my mother knowing about it but it has come out recently that she did and it explains her behaviour towards me.
Really difficult but how would you deal with it?