US Citizen German Spouse Child Custody Issues

So I am married to my German wife and her ex is causing issues with us bringing their daughter to the States. We leave in August so I am trying to do the paperwork for the visas and her ex is constantly making issues. One time he says he will take us to court and then the next he says that he will go to the Jungesamt and we can make an agreement for her daughter to move to the US with us. Now with the visa paperwork ready to mailed to the US Consulate, he has now decided that he will take us to court again. Can anyone maybe give me some insight as to how this custody stuff works in a situation like this?