The problem child needs guidance, not force, to mature into healthy adulthood. Think of yourself, the father, as a coach. Ask yourself, "What would my best coach have done?" You probably won't be too far off the mark.
Be more flexible with your time and attitude to your kids. Try not to set yourself constant strict timetables and parameters. Kids have a wonderful way of living in the moment which means that they don't care what the time is or what may have to be done or what is coming up at another time in the day or the fact that you are tired and hungry. They want to do things now and it's good to not fight them on that all of the time - give them a lot of attention and some flexibility when you can. There will be plenty of times when your schedule will not stretch very far so stretch it on those occasions when you are able to