Their behavior is probably a combination of things. After a divorce kids commonly feel confused, insecure, angry and sometimes guilty. They're very young and verbalizing that may be difficult for them and acting out is their only relief. Another reason may be that they grew up seeing their father treat you like crap and Lord knows what dad is saying when he has them. Does he still have custody? If so the kids may feel abandoned and negative attention is attention none the less.

Whatever the reason you have to let them know that this type of behavior will not be tolerated. This is not a short term easy fix. If the child is throwing a fit, put him in his room and let him throw away. If he's screaming at you, very calmly put him in his room and tell him you'll speak to him when he can speak to you properly. When you discuss this with him when it's finished, don't forget to say "I love you very much, but I will not be treated this way." He WILL get the picture once he sees that you're doing it every time. Make sure you praise him when he's behaving well.