Thank you for your patience with me getting back to you.
Yes, I agree that this woman has some type of personality disorder. She definitely is manipulative. To be able to convince those around her that she is charming and well put together shows she has issues.
It sounds like J has been in trouble with the welfare system but either no one there knows she is sexually assaulting a minor or they can't prove it. If they are not aware of it, would you be comfortable reporting it? I know you mentioned you spoke to the social worker you know but an official report may help even more. You can document what you know and provide dates and times. Write down what is told to you either by J or A or even your son. If you provide details, the police or welfare may pay closer attention. But do not put yourself in danger. If you feel it is too unsafe, then stick to what you are doing.
Can anyone else help you? Has anyone seen the behavior? The more people that report what is going on, the more credibility the report has.
Have you consider involving the police? It may be a bit drastic, but sometimes they operate at a different level than a social services agency might. They may be mandated to investigate immediately as opposed to waiting like welfare.
You can also ask for advice from the police if they cannot act on your report. They may be able to help you figure out how to report J or get enough good evidence to prove she is abusing A.
Beyond that, you can also make your home a safe place for A, if he is willing and open to something like that. Let him know that what is going on his wrong and that he can come to you anytime. If he is ever willing to report what is happening, then you will have a solid case against her.
Let me know if I can help any further,