Brother and sister-in-law attacking niece / grey rock tips for future reference?

[djcleo]

So my eldest sister called me today after sending me screen shots from my niece (her daughter).
Dear brother has again lured one of us in during what should be a time of joy. (first day of college for niece)
No one bothered to tell my brother since he has an established pattern of controlling information and lashing out in vindictive attacks.
We all agreed (sister, me, niece) that brother is again lashing out.
Brother is passive aggressive and uses the knowledge of us to be extra hurtful.
I am wondering what else there is to do. I told sister to have her kids and husband block brother for now, until she had an opportunity to
brace for any further attacks if she chose to confront him.
Sister said to brother "We need to talk".
Brother said "no thanks".
Sister blocked brother.
When someone keeps FOO at a distance and then lashes out and it's a pattern....
What then?
We already have VLC because brother has withdrawn.
Brother moved to another state (we knew he was going to move and it was the neighboring state).
But... he routinely does such things.
Such is a series of his choices.
So we have VLC and then occasionally he reaches out and then we find out he wants something.
And then other times he is extremely malicious.
What can I do to prepare for such an attack?
How do I grey rock?
How can I prepare myself for that?
He hasn't done it to me in a while, but this pattern has been established for a while.
He plays the long game.
And he's on a united unhealthy front with SIL.
He may be hiding that his child is special needs. (yes, we noticed she's developmentally delayed. We still love her.)
So I assume grey rock and medium chill is what's eventually needed if I see him at family gatherings?