Heres what you do man. MAKE A POSITIVE DIFFERENCE IN THAT KIDS LIFE! BE A FATHER FIGURE TO HIM!
Ive done Big Bros/Sisters for years and I have seen a ton of cases like this. Be a father to the kid and let that kid feel being loved by a family. It goes miles man. If you push him away from your kids and they are all friends, then you are doing what everyone has done to that kid his whole life. Take the kid in and include his in your family. Everything will work out from there. I doubt he is a threat to your family. If he has not hit or fights with your kids, then his intentions are honest. Keep a watchful eye but give that kid a chance and help him out.