How best to handle this?

I am the owner of a small locksmith business. I have 3 employees. Myself and one of the employees are service technicians. We are the ones that go out to do the jobs. The other technician (we will refer to him at "T") has been with me for 3 years. I had told him as I was training him that he could call me if he's out on a job and needs help. The problem is this: Even after 3 years and countless hours of training, he still calls me on almost every single job. Most of which I, as the business owner, seem to have to take over for him. I know that he seems not to think of all the possible fixes before calling me. I've talked to him about this, and let him know that he really needs to use his noggin. I am very frustrated in the fact that he does this. If I have to go finish his jobs all the time, what do I need him for (other than me taking time off occasionally). T is also my wife's cousin's son. I can already read it in the comments section: Never hire family. I get that. He is in his late 20s, single dad, and I thought responsible. He was very eager when he started and now is at the point where he is getting too comfortable and not really pulling his weight. One of my shop tech's is very new, and does call me a lot. That is understandable. Does anyone have any advice on how to handle this?