“Two of the three you cite were the sidekicks of violent men. It is extremely unlikely that, had they never met those men, they would ever have killed.”
You can’t be referring to Allitt, so if you think Rose West was a “sidekick” to Fred then you’ve not read any of the trial material, or the books about them or watched any of the interviews with the investigating policemen.
She was the brains and driving force of that partnership, something which the many women they brutalised testified to. She liked to use increasingly large dildos on her female victims until they protested. She’d then tell them they were weak for not being able to take the pain.
Rose killed one of her stepchildren when Fred was still in prison, having physically abused her and her sister over the six months he was inside. That was all on her and the evidence points to many of the other murders being driven by her sexual fetishism.
As for Hindley, even if you choose to believe it was his influence that twisted her, she lured the victims into her car and drove them to the murder sites. She played an active role.