I've been wanting to tell you about my sister. When I was five, X and I would play with our Barbie and Ken dolls on the big wooden dining room table. We used books as room dividers, stood on their sides, piecing the table up into different rooms and apartments for all our Barbies and Kens (we had many). Our dolls had sex together, mashing their pelvises together at a curious diagonal, while standing up. We weren't aware of anything but heterosexuality, but we called the sex "muhfky-fuhfky" (a variant of "fuck"?) One day, my sister X, who was four years older than me, started tearing the heads and arms and legs off my female dolls. She didn't take any off her own. I was very frightened. When I complained, she just showed me where she had heaped my dolls' dismembered limbs and heads. Seeing the torn-off parts unbalanced me, too, as though someone had done that to people. But I couldn't get their arms and legs and heads back on again, and I had no more pleasure playing with my dolls again.
Whoa! I relate to this story. My sister is four years older than me and loved torturing me. Yours sounds a bit more extreme, but I feel your pain!