Child Neglect: Moving with a Child That is Not Mine

My question involves child abuse or neglect in the State of:

I have a 15 year old boy that has been in my care since May, 2013. My own children and I are moving to another suburb and he wishes to move with us. His parents are divorced. His father told him he could not live with him and his mother physically assaulted him and told him to leave her home back in May. She has had contact with him three times since then. She cut off his phone, blocked him on social media and moved twice without telling him where she moved. She basically abandoned him. Neither parent has provided any financial assistance for him but I do receive the Child Tax Benefit from the government as they acknowledge his is with me. He is wanting to attend school in the new community but she will not sign the permission form. The Ministry was involved and told him he could stay where he wanted to which is with me. He has mild turrets which is brought on by stress. He has had no symptoms since moving in with us unless he has had contact with is parents. He almost failed school last year but has brought up his grades from c-'s to A's and B's this year. Can anyone tell me what options I have?