Does he have a good chance of getting custody

My husband is trying to get custody of his 14 year old son who wants to live with him. The mom has been trying to keep him away. She's a shit mom who literally doesn't know how to do anything besides make shitty decisions. His son is bipolar and keeps getting kicked out of school and having suicide attempts because she WONT GIVE HIM HIS MEDICATION!!! We have texts proving that she will not give him his meds because she believes he's faking even though three doctors have diagnosed him with bipolar disorder. My step son also texts me saying his mom got mad and threw a chair at him. The few times we do see him he has had bruises on him. He also said his uncle had PEED ON HIM BEFORE because he got into a fight with him. My husband honestly wants her to have nothing to do with him anymore. He's taking her to court for full custody and to have her pay child support instead of him. She said she doesn't care if he takes her to court because they won't listen to their son because of his mental issues. Is that true? Does he have a chance?

Edit: Yes he's alerted the authorities several times. The child support thing was more something his lawyer said not him.