as far as the visitation goes, only if the children are withheld is it a contempt thing. if he doesnt take them, he doesnt take them. and what he does on his time is his choice. sad but true. with the money aspect of things, the court will with whatever is in your agreement. see if the extra money he owes you will be more than the court battle. and i could be wrong, but nothing your saying here is grounds for full custody.
i agree that he is not being fair or the best parent he could be, but ive learned the hard way that you can only be the best parent YOU can be.