I agree with Drew...stay out of it. We have read way too many cases where another person not involved in the custody case fuels the fire.
We have no way to know what a judge will do. I agree with Drew, they are both better off trying to work something out and staying out of the court room. He has to prove she willingly changed her hours. That email may never even be able to be presented. A judge could certainly change it, a judge could say he can pick them up at their home Friday night, a judge could deny it, who knows.
With the summer, he has to show a change that has occured since that order was put into place and how that change is the best for the kids. If she was working those hours when he was given two weeks, there is no reason for the visitation schedule to change. That would be alot of back and forth for those kids, how is that best for them?
Let him deal with his ex. Quite bluntly, you do not get an opinion about their children and custody.