How to convince parents to let me go natural?

Awww, I feel sad reading your story. Your parents shouldn't be forcing you to damage your hair,especially at 17. I feel sorry for your sisters also. Maybe you can convince your mom to take you to visit a salon and a professional stylist can explain to her the facts about natural hair and its advantages. Unfortunately it seems as though there is a lot of expectation in society to have permed hair. I'm white so I've never had to experience what you're going through but to be perfectly honest I think hair that is natural and healthy, even if it has a bit of a "nappy" texture, looks much better than fake looking, over-processed, fried broken hair. Good luck!