Wages not fair

hi there . ive been working in a small restaurant for nearly two years now as prep chef/wash up/slave but more recently doing the same work as the chefs and working chefs hours giving their responsibilities and everything .the problemis that im getting paid 7 euro an hour which hasn't ever bothered me until now although my coworkers say its not fair because i do so much work for the boos and do unpaid overtime almost everyday ...the problem is a new guy has started on wash up and he is getting paid minimum wage and its his first job and hes my age because i went to school with him and his sister works there to and she told me that their getting paid the same (minimum wage) and that i should ask her . but my boss is a bipolar freak who has never actually fired anyone but makes staff so miserable they leave themselves in my time 8 have left and in the last year her shop has gone through 20 workers on the deli alone so im afraid to ask what should i do ? thanks and is it legal for all the staff to do have an hour extra every evening unpaid because its impossible for the work to get done within the rostered time .