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Hello, I am very sorry that you are having these issues with your step-son, I can understand how distressing this can be for you and your family. First off, unless your step-son acts like this in other setting (e.g. school) this is not ADHD or an Autism
Spectrum Disorder, as the behavior would be present along all settings. There is a possibility that your step-son may have something called Oppositional Defiant Disorder (ODD) where he has sever anger, temper tantrums, delinerately trying to annoy others, arguing with adults, blaming others for his own mistakes, and vindicative. Here is a good link to learn more about ODD if you are curious
What you described regarding her step-son is very serious and you have documented some of the behavior as well. I think family therapy should be encouraged at some point, but for right now your step-son needs to see a Child Psychologist/Psychiatrist for a complete assessment and treatment approach. You can try to talk to your wife about how there is no harm in having her step-son see a Child Psychologist/Psychiatrist as you have shown her documented proof of the behavior and the stories he makes up about you (floating knives). I would agree with you that this behavior is a major sticking point to your marriage and living comfortably in the home and it needs to be addressed with the proper professional, so I think you should encourage that towards your wife. Also explain that you are of course open for family therapy and working on a compromise with all family members so that the home can be peaceful, but you do feel that her son needs to be examined by a mental health professional as his behavior can only worsen without treatment.
I hope this answers your questions and gives you some guidance on this issue. I truly wish you all the best and I hope you and your family can get your step-son the right treatment so that this issue can be overcome quickly. Please let me know if you have any questions or concerns as I am happy to assist and support you regarding this issue.
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