Two Questions. One regarding marriage and the other Regarding work

Hi. My Chinese wife has started an English training center in China. The business is in her name. I want to know if I can help out at the center by teaching a few classes. I'm not going to take a salary of course because it's my wife's business. I will just be teaching a few classes. However, I'm on a marriage visa not a work Z type. Is this illegal? Secondly, my friend wants to get married to his Chinese girlfriend but he's 21. Does he need to get permission from his parents? If so, how?