Yes, please be on the alert. You know some people get worse with certain other people, it is because they have something in them, defected, that makes that happen, and sorry to say it you've now witnessed this flourish first hand. I am guessing partly he is an enabler, partly manipulated and partly just him (with a defect).

I made sure to keep people at a distance because I was ashamed, ashamed and afraid for both their well being and my own, but I never treated anyone badly. But lots of people would tell me afterwards it was as if they could not reach me.

I think there are one sign after another that it is best you should not be in a close relationship right now with your brother as long as he, they, are the way they are.

Also one can also think one does not want to, one simply does not feel like having a close relationship, as this has all cost you too much emotionally.

I think once it gets established the people you do have a closer relationship with in the family, among relatives, without your brother and sister-in-law this will feel better over time. I would also strengthen the bonds I have with other people that are not family and occupy myself doing other things that was, is, of interest to me.

After all the best revenge is to then not think about it no more and to be happy yourself with you and your life.