Problem with Custom Made Fireplace

I have a friend that paid a lot of money to have this custom fireplace put in and they are having problems with it and the contractor won't do anything about it. It has a 6 inch chimney. I am not sure about the height but it runs all the way above the 2 story house so its at least 20 foot. It starts off fine but after about 15 minutes the smoke starts coming into the house and doesn't stop. Is their anything obvious wrong that anyone can tell from the pictures My friend doesn't know what to do. If I need to get some different pictures let me know. Any suggestion?

I don't know about the smoke chamber. I will get better pictures when I can. Where we are from there is no inspection on really anything. I am building a new house and the only inspector I will see is for the septic system. No one will look at my two chimneys. Thanks a lot for the advice. He had a 10 people with no idea telling him how to fix it. Can this fix be done very easy or will that just depend on how its been built?