If both of you are working in full time jobs outside the home and you have a 2 year old child, I do not see where you will find the time and energy to look after a disturbed 12 year old nephew. First of all try and get him professional help from a good psychiatrist. He seems really disturbed. Make sure your nephew goes regularly and follows the treatment suggested. Of course he will benefit from being with loving parental figures, but it will be a long haul. One of his biological parents should take the responsibility of looking after him. His feeling of rejection is very probably, the root of his problems.