1)Chang is someone who has power over him, in the sense that he hold Ed's debt over his head. Ed might doesn't want to get any trouble with Chang in any way that could exacerbate his situation, hence following Chang's order.
2) Waiter? You mean the teenager with the tiny scar at his face?
If you remembered, Chang and Ed called him the little emperor, meaning he's the future leader of the gang in Chinatown. So, in a way, that gives him the advantage /leeway to talk to Ed that way. Cause hes the future boss. There's a mix of hierarchy and respect there. And even Chang said that "the kid wouldn't listen to his parents,so he why would he listen to him"
Well, despite how bad Chang is to Ed, he's the closest one left he ever thought of as family...they grew up together in the same environment and at some period of his life ed depended on Chang and his gang. I'm sure he cant just cut ties all together. It's hard living as minority in a foreign country believe it or not, you feel lot safer and comfortable with people of the same culture, origin, religion etc
the MC with his « older brother » like wtf why does the MC still hang out with him. I mean yes you go there and pay your debt but thats it, no need to accept his dinner invitations, the guy look creepy with his attitude.
Also the waiter at the chinese restaurant, getting all mad because the MC isn’t telling him about his life. Like bitch shut up, the MC has been working his ass off every day to bring money to your boss for like 5 years. Do you think it’s fun? His happy attitude as if everything is going good is somewhat insulting towards the MC.