If this child really makes you angry, as you said, you are already furious. In that case, you can choose not to wronged yourself or not to tutor your children. We can find other excuses. Tell him that you don't have the time and energy to do this kind of thing, or that you have a lot of homework, you are very upset recently or have a lot of things to deal with, so as to get rid of your beautiful relatives in this way.
Another way is to start with children. Suppose your problem is that he doesn't listen to you when you tutor him. In this case, you can choose to ignore him, or let him play his due level when tutoring. Don't restrain him too much. If a relative asks you why you don't help him with his homework, tell him exactly what he did to you. Only in this way can he understand your feelings and may not ask you to do such a thing again in the future.
Also, you can stabilize your mood first. Because you will feel special about this unique experience in the future. Because this is a unique and special experience. At least I want to experience it now. How bear is that Xiong Haizi? When you taught her to do the problem, you actually exercised your ability. If you want to go later. If you are a part-time tutor. I'm talking about when I was in college. At least you have some experience.
As you said, this has caused some troubles in your life. You can choose to learn to refuse the good requests of your loved ones and the unreasonable troubles of your children.