Currently working under my father-in-law and his son. I always feel that he treats me like a servant and wants me to do everything, but his own son never orders me. how

Don't think so, you should know to depend on others. It's not that you have no self-esteem. You should take the initiative to do something. You shouldn't think that you are a relative and deserve special treatment. On the contrary, it is precisely because of this that we should take the initiative to do things, on the one hand, we can exercise ourselves, on the other hand, we can let them see your excellent performance, so that we can pay more attention to you, not complain, learn to be a man and do things with our eyes.