Please give me advice about work!?

You need to learn how to say no. It makes no difference where you work. It is the same everywhere. You need to stand up for yourself but be polite about it. Tell your boss you only want to work 12 hours and possible overtime when emergencies arise. If you don't you will continue to be taken advantage of. Set your expectations and demands on the table. You should not get in trouble for it at all. Training with your sister may be beneficial if it is temporary; consult your handbook for issues on that. Good luck