Hello, I'd like to help you with your question.
It sounds like your daughter in law has taken out her issues on your son and does not seem aware that she is the one with the problems. Because she has no insight, there probably is no way to convince her to get help. A person must see that they have a problem before they would be willing to get help. And at this point, your daughter in law seems convinced that the problem lies with your son.
not mention having legal counsel for your family. If you do not, that would be the first step. Because your daughter in law is unlikely to get help and recover from her issues, then addressing her behavior will have to happen in other ways. Your son needs to be able to protect himself from his wife's destructive behavior towards him. If he is not able to, he may suffer from the stress
of the situation and possibly develop depression, anxiety
or even PTSD.
Besides getting legal help, your son may want to try to be proactive in alerting all the agencies involved about his wife's behavior. He can start a file of paperwork and include any correspondence, tests he has gone through, pictures and any other evidence he has regarding the situation. This file can be used so he does not have to explain himself over and over to the professionals involved. It also may help him in court cases.
Your son may also want to talk to the children and youth protection services about being proactive in caring for his children. Taking steps to gain custody, getting evidence of his wife's abuse of the children, etc. As the children's father, your son should have access to the doctor's reports and to the medical care his children are receiving. If your son can be proactive, he may suffer less from the effects of his wife's behavior towards him.
You may also want to consider family counseling for all of you, but particularly your son. Suffering through being harassed by a family member can cause stress for everyone. Support is vital to dealing with what is going on. And a therapist can not only offer support, but can help each member find ways to care for themselves so the impact of your daughter in law's behavior is less.
The most important part of the situation however is the children. It sounds like your daughter in law is abusing them and using them as pawns in the revenge on your son. Encourage your son to seek custody and surround himself with as much support as possible. It is difficult to go against someone who can manipulate to the point that everyone believes them. But if your son has support and can slowly gather the evidence he needs, he may be able to gain control which would help him and the children.
Here are some resources that may help:
I hope this has helped you,