My ex husband threatened to take our kids and leave out of anger with our court papers. What should I do?

You have a narrow path to follow as you cannot deny him his parenting time rights, but if there is evidence he intends to deprive you of the children, you may want to go to court to change the parenting time to supervised or possibly get the court to otherwise limit him from doing that.  You should see a lawyer.  We don't charge for the first meeting, and there is no obligation to hire us after that meeting, so that might be a thought.