Work Problems

I got told off at work today, again. I was waiting at the counter for customers because my manager said that there has to be someone at the register at all times. He comes up and says, "No no no! We never stand around and do nothing! Go and check on the sale tables!" I, then, calmly replied, "But there won't be anyone at the register." He got all fidgety and said, "Just check on the tables."

He contradicts himself all the time and I get in trouble for it. Also, since the shop is also run by his wife and daughter, it makes it even harder for me because not only do they contradict themselves, they contradict each other.

Personally, I don't understand how you can work with your family members. It would get so frustrating at home if something goes wrong at work. It'd be much nicer (and easier) to leave work problems at work but that would be impossible if the problem people at work come home with you. What do you, guys, think about this issue (ie working with family members)?