How do I protect them?

Since my post on Scheming or Caring, it's been more than a week and I don't think it's helping, because his old habits are still in him.

My instincts tell me that my youngest is going haywire and reverting back to the way he used to feel. While my Ex cannot use threats or the cane he still ignites fear; his presence makes them tense and they seem pressured over their homework and school stuff.
They are still afraid of his reactions to anything and everything. That's an old fear, eventhough this time round, the consequences are not what they used to be before.
But still so afraid.

There can be a irrationality about him(ex), and now I see/hear less,  I don't know how he speaks to the boys(he does more of that when I'm not around or within my oldest's hearing and how it makes them feel.  Is he exercising his narcissistic authority and 'power'(not physical but mental) in other ways, and is it being directed against the youngest boy now?
My youngest is starting to withdraw again, keeping away from his friends and acting 'more hyper'.

I can't seem to reassure them enough that things will work out, and until that time comes, I can only pray that God spares their anxieties.

It's emotional abuse and an even finer line. How do I make anyone understand?