The indirectly indicates that it was a low correlation.

No it doesn't at. It means the correlation is indirect, i.e. alcoholism + factor -> sexual violence. For them to establish a direct correlation they would have to remove the confounding factor of alcoholism, but since all subjects were selected for this risk with no control group without it, they cannot show a direct correlation.

This is an explanatory sentence of the initial one

It is certainly not. They would have established that on the one hand, abusive mothers make it worse, and on the other supportive mothers make it better. It shows a two way effect and strengthens the correlation.

You said it was found to be the key, but it wasn't at all.

Key in families of alcoholic families, together with parental conflict. That is exactly what the study showed, that both the level of neglect from the mother and the conflict between both parents were key contributors to teen sexual violence in children of alcoholic parents. It is as plain as day from the abstract, although it would be much more clear from the data. As soon as I have that I'll repost this because I think it's an important discovery.