WOW, it seems to me that some of this is classic power struggle. You are the adult, and as much as he may be instigating it, your son really needs you to not get sucked into his power struggles. Please read up or reach out for help specifically on diffusing or de-escalating situations with manipulation issues. All things considered, an emotionally healthy person will be in a much better position to “choose life”.
I encourage you to remember (as mentioned earlier) that Hashem chose you as the mother for your son AND your other children. He put them into a family with each other. You know that He knows what He is doing! Lost opportunities are a bitter pill to swallow. Still, I hope you can remember times you were disappointed with a situation initially and in the end things worked out for the best. The whispers and other forms of exclusion are inappropriate and not Torah-true, and I hope your children can learn this and that you can build your children’s self-confidence so that they can weather this storm.
I continue to hope and pray for the best for you and all struggling frum families.