I am so sorry M. Your H seems pretty determined to do anything that he perceives will give him control back. He is clearly not thinking of anyone but himself.
I would probably send a short response telling H that what he did was not acceptable (I am not sure how to word it). Leave it there and don't respond to any spew in response. When your kids get home, sit down and talk and make sure they are OK. You know that your h has not been there for the kids emotionaly in the past so focus all your attention on that.
Completely ignore his email about custody. You have told him numerous times you will not discuss that so I would not even respond.
