How do I get full custody and a child support wage lien?

My ex and I share custody of our two kids. He is emotionally abusive to them and they are getting old enough now that it’s affecting them – they are doing worse in school, acting out at home, and he won’t agree to let me put my younger son in counseling. Will proving emotional abuse be enough to get full custody of them and how do I do that? Can their teachers testify? Also, he’s supposed to be paying me child support because he earns more but he’s never on time. If I do get custody, can I get the child support increased and get it taken out of his paycheck?