Good grief!!
Not for you to fix.
Your husband (absolutely NOT dear to anyone but himself) has behaved absolutely appallingly!
I wouldn’t tolerate that pile of crap from a 2 year old certainly not a bloody grown ass man!
What would I do?
Frankly I’d probably say
“Quit sulking, grow the fuck up, apologise to your child and me for your pathetic toddler tantrum or fuck off!”
“He is stressed at the moment about his business.” Absolutely no excuse and honestly the more you post the worse he sounds!
“But where is the boundary between an argument and abuse? Surely there’s a difference?”
I would say if it happens more than once barring physical assault/violence - which there has been here!
Throwing things is violence, death threats is violence, refusing to talk for several hours is abuse, trying to ban you talking to him is abuse
I’m willing to bet the rest of the time when he doesn’t explode is because you and the children do your damndest to avoid “upsetting” him and you’re all living on eggshells - that is deeply unhealthy for you all especially the children.
And if you think the dc are unaware you’re deluded.
Not at all surprised to discover you are also financially, practically and socially isolated op. Where are your family? Is this type of family how you grew up too? Would your family help you get out of this mess?
Please get help and support to leave.