Need help with 10 year old.

[Chatty100]

I have the most amazing, talented 10 year old who has just turned into a complete nightmare child!! I am separated from his dad (1 year on) but he sees him very regularly. I'm certain that has a lot to do with it. He is so challenging and has both parents at their whit's end. He is very reactive and screams and shouts, slams doors and has no respect at all for either of us. He has recently started playing us off against each other but we are communicating and not letting this happen. He is also a little over weight and wants to loose weight but it's obsessed with food. I really feel like his moods are often effected by food. A lot of our arguments stem from me not letting him have something. It doesn't help that he is allowed more treats with dad and allowed to stay up later. I have three children and the other two are calm, relaxed and no bother what's so ever. I feel like their lives are so effected by the 10 year old and his behaviour. I am just at my whit's end and don't know what to do to help him. Has anyone had any experience of child councillors? I just wonder if that's the route to go down?