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They've been verbally abusive to you and the way to have them butt out is to set your boundaries and be straight forward. Try not to feed into their hostility because they would view that as a power struggle when in fact this is you cutting off your contact with them.
Your husband would have to be supportive to you with this as you're his family now. How he decides to react to his parents is up to him. If you've already sent them emails, you've already expressed your desire to be left in peace. If they are the ones to initiate contact despite your wish, you're not obligated to accept it. Simply remind them that you do not see this being a healthy sort of interaction and that you don't want your kids to see an ugly side from their grandparents. If you do not believe that a compromise will be reached at any time, it would be pointless to expect anything otherwise from them.
If you absolutely must have to speak to them or your sister in law, remain cordial and keep your boundaries. Hopefully your husband had spoken to all of them even if he's a a fixer. Some facts are hard to ignore and this is such a case that needs his support of you and the children.