Hello Segaya,
Shortly, my conclusion from your post is: I would worry about the 2 boys, they could be innocent normal children.
Take it this way: your son is the bad guy, regardless of the fact that he's your son.
And: there are 2 kids! Not 1, but 2!!!
Even if you feel you love your son and the 2 kids, its a...
2-1 situation, like in football...
Better save 2 innocent kids from 1 father whom you know has problems...
Sometimes I feel similarly with my father.
He's my father.
I am loyal, he is not loyal to me.
He too makes "accidents", but not with cars, other things...
All his animals die or "disappear"
So, if I had kids, I wouldn't care about my father, would just make sure he cannot hurt them!
Of course, if you decide to help your grandchildren, then your son must not find out.
I think he could take revenge.
Hmm, I don't know, I would like to help you so much, I think I start to understand your situation...
But, if you "SAVE" your grandkids, what would that mean?
-> do they have a normal mother?
-> you are alone, I think, also with health problems, so you cannot take care of them, I think... it's too hard and they would suffer too
-> they need a good, normal family, where could they go?
-> maybe even a stepfather could be better if he could love and accept them...?
Any way you have to make sure that your son cannot hurt you or the kids.
Of course, if the law could impose some kind of a "distance keeping" for your son... like if he is legally considered a danger to his own kids, it could be easier.
I do understand how painful and how complicated this is to you.