My ex husband has three children, 6, 11, 14. We live 15 minutes from his ex. His ex agreed to let us have the children thrusdays through sundays every other week. She then proceeded after this was in effect to come over and take the children. She does this all the time and in turn hurts the children and us. She verbally abuses my husband and me in front of the children. I have asked her several times to calm down on these occasions for the children are right there. We wish to take her to court for joint custody. What are our chances of obtaing this?

You should be able to. If she is your ex's x and they are your kids why does she have any say anyway?

Sorry I mean my husband and his ex have three children together

Your chances should be good at joint custody I would think. She would have to prove your husband unfit for a Judge to deny you.